Re: [lisp] Updates to draft-ietf-lisp-02.txt

[Damien Saucez <[e-mail]>]

Dino,

Technical comments inline.


The next two paragraphs are my personal opinion and may not be shared by 
Luigi or Olivier.

Once again, why don't you consider versioning at all? Do you have a good 
reason to ignore it? We propose a solution that makes both specification 
and implementation simpler and increase security but you ignore it.

As I already said dozens of time, the control and data-plane format 
could be completely separated. Why do we have the R bits in the Map 
req/rep while it is written, in the respective sections, something like 
"ignore this field, it has no use". IMO, LISP should propose a clean 
protocol with a nice separation between data and control plane. LISP 
proposes to separate the ID and the LOC, so why not go one steps further 
and separate control and data plane?

Back to the specs now ;-)

Dino Farinacci wrote:
> LISPers,
>
> Here are a list of changes I'd like to put into draft-ietf-lisp-02.txt:
>
> (1) Change packet format suggested on list to:
>
>       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>   L / |                       Locator Reach Bits                      |
>   I   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>   S \ |S|E| rsvd-flags|                  Nonce                        |
>   P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> (2) Specify how ECN bits in the TOS header are treated during 
> encapsulation and decapsulation. I have integrated text contributed by 
> David Black from EMC.
>
> (3) Added Probe-bit to the Map-Request and Map-Reply packet formats. 
> Will discuss at IETF. Want to make packet format changes in one step 
> so it is less painful to upgrade the LISP network.
>
> (4) Add the section "Echo Nonce Algorithm" describing how the E-bit 
> (above) is used.
>
> (5) Added a section "LISP Mobile Node Mobility" to the mobility 
> section with an overview to refer to the  draft-meyer-lisp-mn-00.txt 
> draft.
>
> (6) Updated section "Prototype Plans and Status" with more current 
> information.
>
> See enclosed ID and diff file.
>
> I am scheduled to present the 3 locator reachability algorithms I 
> refer to in the draft. The only one documented at this time is the 
> Echo Nonce Algorithm as promised on the list.
>
> Thanks,
> Dino/Dave/Darrel/Vince
>
>
> ------------------------------------------------------------------------
>
> Network Working Group                                       D. Farinacci
> Internet-Draft                                                 V. Fuller
> Intended status: Experimental                                   D. Meyer
> Expires: November 29, 2009 *January 10, 2010*                                       D. Lewis
>                                                            cisco Systems
>                                                             May 28,
>                                                             *July 9,* 2009
>
>                  Locator/ID Separation Protocol (LISP)
>                          draft-ietf-lisp-01.txt
>                          *draft-ietf-lisp-02.txt*
>
> Status of this Memo
>
>    This Internet-Draft is submitted to IETF in full conformance with the
>    provisions of BCP 78 and BCP 79.
>
>    Internet-Drafts are working documents of the Internet Engineering
>    Task Force (IETF), its areas, and its working groups.  Note that
>    other groups may also distribute working documents as Internet-
>    Drafts.
>
>    Internet-Drafts are draft documents valid for a maximum of six months
>    and may be updated, replaced, or obsoleted by other documents at any
>    time.  It is inappropriate to use Internet-Drafts as reference
>    material or to cite them other than as "work in progress."
>
>    The list of current Internet-Drafts can be accessed at
>    http://www.ietf.org/ietf/1id-abstracts.txt.
>
>    The list of Internet-Draft Shadow Directories can be accessed at
>    http://www.ietf.org/shadow.html.
>
>    This Internet-Draft will expire on November 29, 2009. *January 10, 2010.*
>
> Copyright Notice
>
>    Copyright (c) 2009 IETF Trust and the persons identified as the
>    document authors.  All rights reserved.
>
>    This document is subject to BCP 78 and the IETF Trust's Legal
>    Provisions Relating to IETF Documents in effect on the date of
>    publication of this document (http://trustee.ietf.org/license-info).
>    Please review these documents carefully, as they describe your rights
>    and restrictions with respect to this document.
>
> Abstract
>
>    This draft describes a simple, incremental, network-based protocol to
>    implement separation of Internet addresses into Endpoint Identifiers
>    (EIDs) and Routing Locators (RLOCs).  This mechanism requires no
>    changes to host stacks and no major changes to existing database
>    infrastructures.  The proposed protocol can be implemented in a
>    relatively small number of routers.
>
>    This proposal was stimulated by the problem statement effort at the
>    Amsterdam IAB Routing and Addressing Workshop (RAWS), which took
>    place in October 2006.
>
> Table of Contents
>
>    1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  4
>    2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
>    3.  Definition of Terms  . . . . . . . . . . . . . . . . . . . . .  8
>    4.  Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 12
>      4.1.  Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 14
>    5.  Tunneling Details  . . . . . . . . . . . . . . . . . . . . . . 16
>      5.1.  LISP IPv4-in-IPv4 Header Format  . . . . . . . . . . . . . 17
>      5.2.  LISP IPv6-in-IPv6 Header Format  . . . . . . . . . . . . . 18
>      5.3.  Tunnel Header Field Descriptions . . . . . . . . . . . . . 19
>      5.4.  Dealing with Large Encapsulated Packets  . . . . . . . . . 20 *21*
>        5.4.1.  A Stateless Solution to MTU Handling . . . . . . . . . 21
>        5.4.2.  A Stateful Solution to MTU Handling  . . . . . . . . . 22
>    6.  EID-to-RLOC Mapping  . . . . . . . . . . . . . . . . . . . . . 23
>      6.1.  LISP IPv4 and IPv6 Control Plane Packet Formats  . . . . . 23
>        6.1.1.  LISP Packet Type Allocations . . . . . . . . . . . . . 25
>        6.1.2.  Map-Request Message Format . . . . . . . . . . . . . . 25
>        6.1.3.  EID-to-RLOC UDP Map-Request Message  . . . . . . . . . 27
>        6.1.4.  Map-Reply Message Format . . . . . . . . . . . . . . . 28
>        6.1.5.  EID-to-RLOC UDP Map-Reply Message  . . . . . . . . . . 31
>        6.1.6.  Map-Register Message Format  . . . . . . . . . . . . . 32
>      6.2.  Routing Locator Selection  . . . . . . . . . . . . . . . . 34
>      6.3.  Routing Locator Reachability . . . . . . . . . . . . . . . 35
>        *6.3.1.  Echo Nonce Algorithm . . . . . . . . . . . . . . . . . 37*
>      6.4.  Routing Locator Hashing  . . . . . . . . . . . . . . . . . 37 *38*
>      6.5.  Changing the Contents of EID-to-RLOC Mappings  . . . . . . 38 *39*
>        6.5.1.  Clock Sweep  . . . . . . . . . . . . . . . . . . . . . 39
>        6.5.2.  Solicit-Map-Request (SMR)  . . . . . . . . . . . . . . 39 *40*
>    7.  Router Performance Considerations  . . . . . . . . . . . . . . 41 *42*
>    8.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 42 *43*
>      8.1.  First-hop/Last-hop Tunnel Routers  . . . . . . . . . . . . 43 *44*
>      8.2.  Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 43 *44*
>      8.3.  ISP Provider-Edge (PE) Tunnel Routers  . . . . . . . . . . 44 *45*
>    9.  Traceroute Considerations  . . . . . . . . . . . . . . . . . . 45 *46*
>      9.1.  IPv6 Traceroute  . . . . . . . . . . . . . . . . . . . . . 46 *47*
>      9.2.  IPv4 Traceroute  . . . . . . . . . . . . . . . . . . . . . 46 *47*
>      9.3.  Traceroute using Mixed Locators  . . . . . . . . . . . . . 46 *47*
>    10. Mobility Considerations  . . . . . . . . . . . . . . . . . . . 48 *49*
>      10.1. Site Mobility  . . . . . . . . . . . . . . . . . . . . . . 48 *49*
>      10.2. Slow Endpoint Mobility . . . . . . . . . . . . . . . . . . 48 *49*
>      10.3. Fast Endpoint Mobility . . . . . . . . . . . . . . . . . . 48 *49*
>      10.4. Fast Network Mobility  . . . . . . . . . . . . . . . . . . 50 *51
>      10.5. LISP Mobile Node Mobility  . . . . . . . . . . . . . . . . 51*
>    11. Multicast Considerations . . . . . . . . . . . . . . . . . . . 51 *53*
>    12. Security Considerations  . . . . . . . . . . . . . . . . . . . 52 *54*
>    13. Prototype Plans and Status . . . . . . . . . . . . . . . . . . 53 *55*
>    14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 56 *58*
>      14.1. Normative References . . . . . . . . . . . . . . . . . . . 56 *58*
>      14.2. Informative References . . . . . . . . . . . . . . . . . . 57 *59*
>    Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 60 *62*
>    Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 61 *63*
>
> 1.  Requirements Notation
>
>    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
>    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
>    document are to be interpreted as described in [RFC2119].
>
> 2.  Introduction
>
>    Many years of discussion about the current IP routing and addressing
>    architecture have noted that its use of a single numbering space (the
>    "IP address") for both host transport session identification and
>    network routing creates scaling issues (see [CHIAPPA] and [RFC1498]).
>    A number of scaling benefits would be realized by separating the
>    current IP address into separate spaces for Endpoint Identifiers
>    (EIDs) and Routing Locators (RLOCs); among them are:
>
>    1.  Reduction of routing table size in the "default-free zone" (DFZ).
>        Use of a separate numbering space for RLOCs will allow them to be
>        assigned topologically (in today's Internet, RLOCs would be
>        assigned by providers at client network attachment points),
>        greatly improving aggregation and reducing the number of
>        globally-visible, routable prefixes.
>
>    2.  More cost-effective multihoming for sites that connect to
>        different service providers where they can control their own
>        policies for packet flow into the site without using extra
>        routing table resources of core routers.
>
>    3.  Easing of renumbering burden when clients change providers.
>        Because host EIDs are numbered from a separate, non-provider-
>        assigned and non-topologically-bound space, they do not need to
>        be renumbered when a client site changes its attachment points to
>        the network.
>
>    4.  Traffic engineering capabilities that can be performed by network
>        elements and do not depend on injecting additional state into the
>        routing system.  This will fall out of the mechanism that is used
>        to implement the EID/RLOC split (see Section 4).
>
>    5.  Mobility without address changing.  Existing mobility mechanisms
>        will be able to work in a locator/ID separation scenario.  It
>        will be possible for a host (or a collection of hosts) to move to
>        a different point in the network topology either retaining its
>        home-based address or acquiring a new address based on the new
>        network location.  A new network location could be a physically
>        different point in the network topology or the same physical
>        point of the topology with a different provider.
>
>    This draft describes protocol mechanisms to achieve the desired
>    functional separation.  For flexibility, the mechanism used for
>    forwarding packets is decoupled from that used to determine EID to
>    RLOC mappings.  This document covers the former.  For the later, see
>    [CONS], [ALT], *[EMACS],* [RPMD], and [NERD].  This work is in response
>    to and intended to address the problem statement that came out of the
>    RAWS effort [RFC4984].
>
>    The Routing and Addressing problem statement can be found in [RADIR].
>
>    This draft focuses on a router-based solution.  Building the solution
>    into the network will facilitate incremental deployment of the
>    technology on the Internet.  Note that while the detailed protocol
>    specification and examples in this document assume IP version 4
>    (IPv4), there is nothing in the design that precludes use of the same
>    techniques and mechanisms for IPv6.  It should be possible for IPv4
>    packets to use IPv6 RLOCs and for IPv6 EIDs to be mapped to IPv4
>    RLOCs.
>
>    Related work on host-based solutions is described in Shim6 [SHIM6]
>    and HIP [RFC4423].  Related work on a router-based solution is
>    described in [GSE].  This draft attempts to not compete or overlap
>    with such solutions and the proposed protocol changes are expected to
>    complement a host-based mechanism when Traffic Engineering
>    functionality is desired.
>
>    Some of the design goals of this proposal include:
>
>    1.  Require no hardware or software changes to end-systems (hosts).
>
>    2.  Minimize required changes to Internet infrastructure.
>
>    3.  Be incrementally deployable.
>
>    4.  Require no router hardware changes.
>
>    5.  Minimize the number of routers which have to be modified.  In
>        particular, most customer site routers and no core routers
>        require changes.
>
>    6.  Minimize router software changes in those routers which are
>        affected.
>
>    7.  Avoid or minimize packet loss when EID-to-RLOC mappings need to
>        be performed.
>
>    There are 4 variants of LISP, which differ along a spectrum of strong
>    to weak dependence on the topological nature and possible need for
>    routability of EIDs.  The variants are:
>
>    LISP 1:  uses EIDs that are routable through the RLOC topology for
>       bootstrapping EID-to-RLOC mappings.  [LISP1] This was intended as
>       a prototyping mechanism for early protocol implementation.  It is
>       now deprecated and should not be deployed.
>
>    LISP 1.5:  uses EIDs that are routable for bootstrapping EID-to-RLOC
>       mappings; such routing is via a separate topology.
>
>    LISP 2:  uses EIDS that are not routable and EID-to-RLOC mappings are
>       implemented within the DNS.  [LISP2]
>
>    LISP 3:  uses non-routable EIDs that are used as lookup keys for a
>       new EID-to-RLOC mapping database.  Use of Distributed Hash Tables
>       [DHTs] [LISPDHT] to implement such a database would be an area to
>       explore.  Other examples of new mapping database services are
>       [CONS], [ALT], [RPMD], [NERD], and [APT].
>
>    This document on LISP 1.5, and LISP 3 variants, both of which rely on
>    a router-based distributed cache and database for EID-to-RLOC
>    mappings.  The LISP 1.0 mechanism works but does not allow reduction
>    of routing information in the default-free-zone of the Internet.  The
>    LISP 2 mechanisms are put on hold and may never come to fruition
>    since it is not architecturally pure to have routing depend on
>    directory and directory depend on routing.  The LISP 3 mechanisms
>    will be documented elsewhere but may use the control-plane options
>    specified in this specification.
>
> 3.  Definition of Terms
>
>    Provider Independent (PI) Addresses:   an address block assigned from
>       a pool where blocks are not associated with any particular
>       location in the network (e.g. from a particular service provider),
>       and is therefore not topologically aggregatable in the routing
>       system.
>
>    Provider Assigned (PA) Addresses:   a block of IP addresses that are
>       assigned to a site by each service provider to which a site
>       connects.  Typically, each block is sub-block of a service
>       provider CIDR block and is aggregated into the larger block before
>       being advertised into the global Internet.  Traditionally, IP
>       multihoming has been implemented by each multi-homed site
>       acquiring its own, globally-visible prefix.  LISP uses only
>       topologically-assigned and aggregatable address blocks for RLOCs,
>       eliminating this demonstrably non-scalable practice.
>
>    Routing Locator (RLOC):   the IPv4 or IPv6 address of an egress
>       tunnel router (ETR).  It is the output of a EID-to-RLOC mapping
>       lookup.  An EID maps to one or more RLOCs.  Typically, RLOCs are
>       numbered from topologically-aggregatable blocks that are assigned
>       to a site at each point to which it attaches to the global
>       Internet; where the topology is defined by the connectivity of
>       provider networks, RLOCs can be thought of as PA addresses.
>       Multiple RLOCs can be assigned to the same ETR device or to
>       multiple ETR devices at a site.
>
>    Endpoint ID (EID):   a 32-bit (for IPv4) or 128-bit (for IPv6) value
>       used in the source and destination address fields of the first
>       (most inner) LISP header of a packet.  The host obtains a
>       destination EID the same way it obtains an destination address
>       today, for example through a DNS lookup or SIP exchange.  The
>       source EID is obtained via existing mechanisms used to set a
>       host's "local" IP address.  An EID is allocated to a host from an
>       EID-prefix block associated with the site where the host is
>       located.  An EID can be used by a host to refer to other hosts.
>       EIDs MUST NOT be used as LISP RLOCs.  Note that EID blocks may be
>       assigned in a hierarchical manner, independent of the network
>       topology, to facilitate scaling of the mapping database.  In
>       addition, an EID block assigned to a site may have site-local
>       structure (subnetting) for routing within the site; this structure
>       is not visible to the global routing system.  When used in
>       discussions with other Locator/ID separation proposals, a LISP EID
>       will be called a "LEID".  Throughout this document, any references
>       to "EID" refers to an LEID.
>
>    EID-prefix:   A power-of-2 block of EIDs which are allocated to a
>       site by an address allocation authority.  EID-prefixes are
>       associated with a set of RLOC addresses which make up a "database
>       mapping".  EID-prefix allocations can be broken up into smaller
>       blocks when an RLOC set is to be associated with the smaller EID-
>       prefix.  A globally routed address block (whether PI or PA) is not
>       an EID-prefix.  However, a globally routed address block may be
>       removed from global routing and reused as an EID-prefix.  A site
>       that receives an explicitly allocated EID-prefix may not use that
>       EID-prefix as a globally routed prefix assigned to RLOCs.
>
>    End-system:   is an IPv4 or IPv6 device that originates packets with
>       a single IPv4 or IPv6 header.  The end-system supplies an EID
>       value for the destination address field of the IP header when
>       communicating globally (i.e. outside of its routing domain).  An
>       end-system can be a host computer, a switch or router device, or
>       any network appliance.
>
>    Ingress Tunnel Router (ITR):   a router which accepts an IP packet
>       with a single IP header (more precisely, an IP packet that does
>       not contain a LISP header).  The router treats this "inner" IP
>       destination address as an EID and performs an EID-to-RLOC mapping
>       lookup.  The router then prepends an "outer" IP header with one of
>       its globally-routable RLOCs in the source address field and the
>       result of the mapping lookup in the destination address field.
>       Note that this destination RLOC may be an intermediate, proxy
>       device that has better knowledge of the EID-to-RLOC mapping closer
>       to the destination EID.  In general, an ITR receives IP packets
>       from site end-systems on one side and sends LISP-encapsulated IP
>       packets toward the Internet on the other side.
>
>       Specifically, when a service provider prepends a LISP header for
>       Traffic Engineering purposes, the router that does this is also
>       regarded as an ITR.  The outer RLOC the ISP ITR uses can be based
>       on the outer destination address (the originating ITR's supplied
>       RLOC) or the inner destination address (the originating hosts
>       supplied EID).
>
>    TE-ITR:   is an ITR that is deployed in a service provider network
>       that prepends an additional LISP header for Traffic Engineering
>       purposes.
>
>    Egress Tunnel Router (ETR):   a router that accepts an IP packet
>       where the destination address in the "outer" IP header is one of
>       its own RLOCs.  The router strips the "outer" header and forwards
>       the packet based on the next IP header found.  In general, an ETR
>       receives LISP-encapsulated IP packets from the Internet on one
>       side and sends decapsulated IP packets to site end-systems on the
>       other side.  ETR functionality does not have to be limited to a
>       router device.  A server host can be the endpoint of a LISP tunnel
>       as well.
>
>    TE-ETR:   is an ETR that is deployed in a service provider network
>       that strips an outer LISP header for Traffic Engineering purposes.
>
>    xTR:   is a reference to an ITR or ETR when direction of data flow is
>       not part of the context description. xTR refers to the router that
>       is the tunnel endpoint.  Used synonymously with the term "Tunnel
>       Router".  For example, "An xTR can be located at the Customer Edge
>       (CE) router", meaning both ITR and ETR functionality is at the CE
>       router.
>
>    EID-to-RLOC Cache:   a short-lived, on-demand table in an ITR that
>       stores, tracks, and is responsible for timing-out and otherwise
>       validating EID-to-RLOC mappings.  This cache is distinct from the
>       full "database" of EID-to-RLOC mappings, it is dynamic, local to
>       the ITR(s), and relatively small while the database is
>       distributed, relatively static, and much more global in scope.
>
>    EID-to-RLOC Database:   a global distributed database that contains
>       all known EID-prefix to RLOC mappings.  Each potential ETR
>       typically contains a small piece of the database: the EID-to-RLOC
>       mappings for the EID prefixes "behind" the router.  These map to
>       one of the router's own, globally-visible, IP addresses.
>
>    Recursive Tunneling:   when a packet has more than one LISP IP
>       header.  Additional layers of tunneling may be employed to
>       implement traffic engineering or other re-routing as needed.  When
>       this is done, an additional "outer" LISP header is added and the
>       original RLOCs are preserved in the "inner" header.  Any
>       references to tunnels in this specification refers to dynamic
>       encapsulating tunnels and never are they staticly configured.
>
>    Reencapsulating Tunnels:   when a packet has no more than one LISP IP
>       header (two IP headers total) and when it needs to be diverted to
>       new RLOC, an ETR can decapsulate the packet (remove the LISP
>       header) and prepend a new tunnel header, with new RLOC, on to the
>       packet.  Doing this allows a packet to be re-routed by the re-
>       encapsulating router without adding the overhead of additional
>       tunnel headers.  Any references to tunnels in this specification
>       refers to dynamic encapsulating tunnels and never are they
>       staticly configured.
>
>    LISP Header:   a term used in this document to refer to the outer
>       IPv4 or IPv6 header, a UDP header, and a LISP header, an ITR
>       prepends or an ETR strips.
>
>    Address Family Indicator (AFI):   a term used to describe an address
>       encoding in a packet.  An address family currently pertains to an
>       IPv4 or IPv6 address.  See [AFI] for details.
>
>    Negative Mapping Entry:   also known as a negative cache entry, is an
>       EID-to-RLOC entry where an EID-prefix is advertised or stored with
>       no RLOCs.  That is, the locator-set for the EID-to-RLOC entry is
>       empty or has an encoded locator count of 0.  This type of entry
>       could be used to describe a prefix from a non-LISP site, which is
>       explicitly not in the mapping database.  There are a set of well
>       defined actions that are encoded in a Negative Map-Reply.
>
>    Data Probe:   a LISP-encapsulated data packet where the inner header
>       destination address equals the outer header destination address
>       used to trigger a Map-Reply by a decapsulating ETR.  In addition,
>       the original packet is decapsulated and delivered to the
>       destination host.  A Data Probe is used in some of the mapping
>       database designs to "probe" or request a Map-Reply from an ETR; in
>       other cases, Map-Requests are used.  See each mapping database
>       design for details.
>
> 4.  Basic Overview
>
>    One key concept of LISP is that end-systems (hosts) operate the same
>    way they do today.  The IP addresses that hosts use for tracking
>    sockets, connections, and for sending and receiving packets do not
>    change.  In LISP terminology, these IP addresses are called Endpoint
>    Identifiers (EIDs).
>
>    Routers continue to forward packets based on IP destination
>    addresses.  When a packet is LISP encapsulated, these addresses are
>    referred to as Routing Locators (RLOCs).  Most routers along a path
>    between two hosts will not change; they continue to perform routing/
>    forwarding lookups on the destination addresses.  For routers between
>    the source host and the ITR as well as routers from the ETR to the
>    destination host, the destination address is an EID.  For the routers
>    between the ITR and the ETR, the destination address is an RLOC.
>
>    This design introduces "Tunnel Routers", which prepend LISP headers
>    on host-originated packets and strip them prior to final delivery to
>    their destination.  The IP addresses in this "outer header" are
>    RLOCs.  During end-to-end packet exchange between two Internet hosts,
>    an ITR prepends a new LISP header to each packet and an egress tunnel
>    router strips the new header.  The ITR performs EID-to-RLOC lookups
>    to determine the routing path to the the ETR, which has the RLOC as
>    one of its IP addresses.
>
>    Some basic rules governing LISP are:
>
>    o  End-systems (hosts) only send to addresses which are EIDs.  They
>       don't know addresses are EIDs versus RLOCs but assume packets get
>       to LISP routers, which in turn, deliver packets to the destination
>       the end-system has specified.
>
>    o  EIDs are always IP addresses assigned to hosts.
>
>    o  LISP routers mostly deal with Routing Locator addresses.  See
>       details later in Section 4.1 to clarify what is meant by "mostly".
>
>    o  RLOCs are always IP addresses assigned to routers; preferably,
>       topologically-oriented addresses from provider CIDR blocks.
>
>    o  When a router originates packets it may use as a source address
>       either an EID or RLOC.  When acting as a host (e.g. when
>       terminating a transport session such as SSH, TELNET, or SNMP), it
>       may use an EID that is explicitly assigned for that purpose.  An
>       EID that identifies the router as a host MUST NOT be used as an
>       RLOC; an EID is only routable within the scope of a site.  A
>       typical BGP configuration might demonstrate this "hybrid" EID/RLOC
>       usage where a router could use its "host-like" EID to terminate
>       iBGP sessions to other routers in a site while at the same time
>       using RLOCs to terminate eBGP sessions to routers outside the
>       site.
>
>    o  EIDs are not expected to be usable for global end-to-end
>       communication in the absence of an EID-to-RLOC mapping operation.
>       They are expected to be used locally for intra-site communication.
>
>    o  EID prefixes are likely to be hierarchically assigned in a manner
>       which is optimized for administrative convenience and to
>       facilitate scaling of the EID-to-RLOC mapping database.  The
>       hierarchy is based on a address allocation hierarchy which is not
>       dependent on the network topology.
>
>    o  EIDs may also be structured (subnetted) in a manner suitable for
>       local routing within an autonomous system.
>
>    An additional LISP header may be prepended to packets by a transit
>    router (i.e.  TE-ITR) when re-routing of the path for a packet is
>    desired.  An obvious instance of this would be an ISP router that
>    needs to perform traffic engineering for packets in flow through its
>    network.  In such a situation, termed Recursive Tunneling, an ISP
>    transit acts as an additional ingress tunnel router and the RLOC it
>    uses for the new prepended header would be either an TE-ETR within
>    the ISP (along intra-ISP traffic engineered path) or in an TE-ETR
>    within another ISP (an inter-ISP traffic engineered path, where an
>    agreement to build such a path exists).
>
>    This specification mandates that no more than two LISP headers get
>    prepended to a packet.  This avoids excessive packet overhead as well
>    as possible encapsulation loops.  It is believed two headers is
>    sufficient, where the first prepended header is used at a site for
>    Location/Identity separation and second prepended header is used
>    inside a service provider for Traffic Engineering purposes.
>
>    Tunnel Routers can be placed fairly flexibly in a multi-AS topology.
>    For example, the ITR for a particular end-to-end packet exchange
>    might be the first-hop or default router within a site for the source
>    host.  Similarly, the egress tunnel router might be the last-hop
>    router directly-connected to the destination host.  Another example,
>    perhaps for a VPN service out-sourced to an ISP by a site, the ITR
>    could be the site's border router at the service provider attachment
>    point.  Mixing and matching of site-operated, ISP-operated, and other
>    tunnel routers is allowed for maximum flexibility.  See Section 8 for
>    more details.
>
> 4.1.  Packet Flow Sequence
>
>    This section provides an example of the unicast packet flow with the
>    following conditions:
>
>    o  Source host "host1.abc.com" is sending a packet to
>       "host2.xyz.com", exactly what host1 would do if the site was not
>       using LISP.
>
>    o  Each site is multi-homed, so each tunnel router has an address
>       (RLOC) assigned from the service provider address block for each
>       provider to which that particular tunnel router is attached.
>
>    o  The ITR(s) and ETR(s) are directly connected to the source and
>       destination, respectively.
>
>    o  Data Probes are used to solicit Map-Replies versus using Map-
>       Requests.  And the Data Probes are sent on the underlying topology
>       (the LISP 1.0 variant) but could also be sent over an alternative
>       topology (the LISP 1.5 variant) as it would in [ALT].
>
>    Client host1.abc.com wants to communicate with server host2.xyz.com:
>
>    1.  host1.abc.com wants to open a TCP connection to host2.xyz.com.
>        It does a DNS lookup on host2.xyz.com.  An A/AAAA record is
>        returned.  This address is used as the destination EID and the
>        locally-assigned address of host1.abc.com is used as the source
>        EID.  An IPv4 or IPv6 packet is built using the EIDs in the IPv4
>        or IPv6 header and sent to the default router.
>
>    2.  The default router is configured as an ITR.  The ITR must be able
>        to map the EID destination to an RLOC of the ETR at the
>        destination site.  The ITR prepends a LISP header to the packet,
>        with one of its RLOCs as the source IPv4 or IPv6 address.  The
>        destination EID from the original packet header is used as the
>        destination IPv4 or IPv6 in the prepended LISP header.
>        Subsequent packets, where the outer destination address is the
>        destination EID will be sent until EID-to-RLOC mapping is
>        learned.
>
>    3.  In LISP 1, the packet is routed through the Internet as it is
>        today.  In LISP 1.5, the packet is routed on a different topology
>        which may have EID prefixes distributed and advertised in an
>        aggregatable fashion.  In either case, the packet arrives at the
>        ETR.  The router is configured to "punt" the packet to the
>        router's processor.  See Section 7 for more details.  For LISP
>        2.0 and 3.0, the behavior is not fully defined yet.
>
>    4.  The LISP header is stripped so that the packet can be forwarded
>        by the router control plane.  The router looks up the destination
>        EID in the router's EID-to-RLOC database (not the cache, but the
>        configured data structure of RLOCs).  An EID-to-RLOC Map-Reply
>        message is originated by the ETR and is addressed to the source
>        RLOC in the LISP header of the original packet (this is the ITR).
>        The source RLOC of the Map-Reply is one of the ETR's RLOCs.
>
>    5.  The ITR receives the Map-Reply message, parses the message (to
>        check for format validity) and stores the mapping information
>        from the packet.  This information is put in the ITR's EID-to-
>        RLOC mapping cache (this is the on-demand cache, the cache where
>        entries time out due to inactivity).
>
>    6.  Subsequent packets from host1.abc.com to host2.xyz.com will have
>        a LISP header prepended by the ITR using the appropriate RLOC as
>        the LISP header destination address learned from the ETR.  Note,
>        the packet may be sent to a different ETR than the one which
>        returned the Map-Reply due to the source site's hashing policy or
>        the destination site's locator-set policy.
>
>    7.  The ETR receives these packets directly (since the destination
>        address is one of its assigned IP addresses), strips the LISP
>        header and forwards the packets to the attached destination host.
>
>    In order to eliminate the need for a mapping lookup in the reverse
>    direction, an ETR MAY create a cache entry that maps the source EID
>    (inner header source IP address) to the source RLOC (outer header
>    source IP address) in a received LISP packet.  Such a cache entry is
>    termed a "gleaned" mapping and only contains a single RLOC for the
>    EID in question.  More complete information about additional RLOCs
>    SHOULD be verified by sending a LISP Map-Request for that EID.  Both
>    ITR and the ETR may also influence the decision the other makes in
>    selecting an RLOC.  See Section 6 for more details.
>
> 5.  Tunneling Details
>
>    This section describes the LISP Data Message which defines the
>    tunneling header used to encapsulate IPv4 and IPv6 packets which
>    contain EID addresses.  Even though the following formats illustrate
>    IPv4-in-IPv4 and IPv6-in-IPv6 encapsulations, the other 2
>    combinations are supported as well.
>
>    Since additional tunnel headers are prepended, the packet becomes
>    larger and in theory can exceed the MTU of any link traversed from
>    the ITR to the ETR.  It is recommended, in IPv4 that packets do not
>    get fragmented as they are encapsulated by the ITR.  Instead, the
>    packet is dropped and an ICMP Too Big message is returned to the
>    source.
>
>    Based on informal surveys of large ISP traffic patterns, it appears
>    that most transit paths can accommodate a path MTU of at least 4470
>    bytes.  The exceptions, in terms of data rate, number of hosts
>    affected, or any other metric are expected to be vanishingly small.
>
>    To address MTU concerns, mainly raised on the RRG mailing list, the
>    LISP deployment process will include collecting data during its pilot
>    phase to either verify or refute the assumption about minimum
>    available MTU.  If the assumption proves true and transit networks
>    with links limited to 1500 byte MTUs are corner cases, it would seem
>    more cost-effective to either upgrade or modify the equipment in
>    those transit networks to support larger MTUs or to use existing
>    mechanisms for accommodating packets that are too large.
>
>    For this reason, there is currently no plan for LISP to add any new
>    additional, complex mechanism for implementing fragmentation and
>    reassembly in the face of limited-MTU transit links.  If analysis
>    during LISP pilot deployment reveals that the assumption of
>    essentially ubiquitous, 4470+ byte transit path MTUs, is incorrect,
>    then LISP can be modified prior to protocol standardization to add
>    support for one of the proposed fragmentation and reassembly schemes.
>    Note that two simple existing schemes are detailed in Section 5.4.
>
>   

> 5.1.  LISP IPv4-in-IPv4 Header Format
>
>         0                   1                   2                   3
>         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |Version|  IHL  |Type of Service|          Total Length         |
>     /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |   |         Identification        |Flags|      Fragment Offset    |
>    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    OH  |  Time to Live | Protocol = 17 |         Header Checksum       |
>    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |   |                    Source Routing Locator                     |
>     \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      \ |                 Destination Routing Locator                   |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |       Source Port = xxxx      |       Dest Port = 4341        |
>    UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      \ |           UDP Length          |        UDP Checksum           |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    L / |S| *|*                       Locator Reach Bits                      |
>    I   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    S \ | *|S|E| rsvd-flags|*                  Nonce                        |
>    P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |Version|  IHL  |Type of Service|          Total Length         |
>     /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |   |         Identification        |Flags|      Fragment Offset    |
>    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    IH  |  Time to Live |    Protocol   |         Header Checksum       |
>    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |   |                           Source EID                          |
>     \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      \ |                         Destination EID                       |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> 5.2.  LISP IPv6-in-IPv6 Header Format
>
>         0                   1                   2                   3
>         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |Version| Traffic Class |           Flow Label                  |
>     /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |   |         Payload Length        | Next Header=17|   Hop Limit   |
>    v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                                                               |
>    O   +                                                               +
>    u   |                                                               |
>    t   +                     Source Routing Locator                    +
>    e   |                                                               |
>    r   +                                                               +
>        |                                                               |
>    H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    d   |                                                               |
>    r   +                                                               +
>        |                                                               |
>    ^   +                  Destination Routing Locator                  +
>    |   |                                                               |
>     \  +                                                               +
>      \ |                                                               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |       Source Port = xxxx      |       Dest Port = 4341        |
>    UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      \ |           UDP Length          |        UDP Checksum           |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    L / |S| *|*                       Locator Reach Bits                      |
>    I   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    S \ | *|S|E| rsvd-flags|*                  Nonce                        |
>    P   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |Version| Traffic Class |           Flow Label                  |
>     /  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    /   |         Payload Length        |  Next Header  |   Hop Limit   |
>    v   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                                                               |
>    I   +                                                               +
>    n   |                                                               |
>    n   +                          Source EID                           +
>    e   |                                                               |
>    r   +                                                               +
>        |                                                               |
>    H   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    d   |                                                               |
>    r   +                                                               +
>        |                                                               |
>    ^   +                        Destination EID                        +
>    \   |                                                               |
>     \  +                                                               +
>      \ |                                                               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> 5.3.  Tunnel Header Field Descriptions
>
>    IH Header:  is the inner header, preserved from the datagram received
>       from the originating host.  The source and destination IP
>       addresses are EIDs.
>
>    OH Header:  is the outer header prepended by an ITR.  The address
>       fields contain RLOCs obtained from the ingress router's EID-to-
>       RLOC cache.  The IP protocol number is "UDP (17)" from [RFC0768].
>       The DF bit of the Flags field is set to 0.
>
>    UDP Header:  contains a ITR selected source port when encapsulating a
>       packet.  See Section 6.4 for details on the hash algorithm used
>       select a source port based on the 5-tuple of the inner header.
>       The destination port MUST be set to the well-known IANA assigned
>       port value 4341.
>
>    UDP Checksum:  this field 
typo
> field 

> MUST
SHOULD
>  be transmitted as 0 and ignored
>       on receipt by the ETR.  Note, even when the UDP checksum is
>       transmitted as 0 an intervening NAT device can recalculate the
>       checksum and rewrite the UDP checksum field to non-zero.  For
>       performance reasons, the ETR MUST ignore the checksum and 

> MUST 
SHOULD
> not
>       do a checksum computation.
>   
it would be better to have: if checksum is not computed, checksum MUST 
be set to 0. Otherwise, the value MUST be the result of the checksum 
computation. Then, if someone desires to check UDP, it can iif it is 
non-zero.
>    UDP Length:  for an IPv4 encapsulated packet, the inner header Total
>       Length plus the UDP and LISP header lengths are used.  For an IPv6
>       encapsulated packet, the inner header Payload Length plus the size
>       of the IPv6 header (40 bytes) plus the size of the UDP and LISP
>       headers are used.  The UDP header length is 8 bytes.  The LISP
>       header length is 8 bytes when no loc-reach-bit header extensions
>       are used.
>
>    S: this is the Solicit-Map-Request (SMR) bit.  See section
>       Section 6.5.2 for details.
>
>    LISP Locator Reach Bits:  in the LISP header are set by an ITR to
>       indicate to an ETR the reachability of the Locators in the source
>       site.  Each RLOC in a Map-Reply is assigned an ordinal value from
>       0 to n-1 (when there are n RLOCs in a mapping entry).  The Locator
>       Reach Bits are numbered from 0 to n-1 from the right significant
>       bit of the 31-bit *32-bit* field.  When a bit is set to 1, the ITR is
>       indicating to the ETR the RLOC associated with the bit ordinal is
>       reachable.  See Section 6.3 for details on how an ITR can
>       determine other ITRs at the site are reachable.  When a site has
>       multiple EID-prefixes which result in multiple mappings (where
>       each could have a different locator-set), the Locator Reach Bits
>       setting in an encapsulated packet MUST reflect the mapping for the
>       EID-prefix that the inner-header source EID address matches.
>
>    *S: this is the Solicit-Map-Request (SMR) bit.  See section
>       Section 6.5.2 for details.
>
>    E: this is the echo-nonce-request bit.  See section Section 6.3.1 for
>       details.
>
>    rsvd-flags:  this 6-bit field is reserved for future flag use.  It is
>       set to 0 on transmit and ignored on receipt.*
>
>    LISP Nonce:  is a 32-bit *24-bit* value that is randomly generated by an ITR.
>       It is used to test route-returnability when xTRs exchange
>       encapsulated data packets with the SMR bit set, Data-Probe, Map-
>       Request, or Map-Reply messages.
>
>    When doing Recursive Tunneling: *Tunneling or ITR/PTR encapsulation:*
>
>    o  The OH header Time to Live field (or Hop Limit field, in case of
>       IPv6) MUST be copied from the IH header Time to Live field.
>
>   
Why not with a -1? Do you consider that -1 has been done before being 
processed by the LISP code? If yes, should be explicitly written. If no 
-1, a loop can happen.
>    o  The OH header Type of Service field (or the Traffic Class field,
>       in the case of IPv6) SHOULD be copied from the IH header Type of
>       Service field (with one caveat, see below).
>
>    When doing Re-encapsulated Tunneling:
>
>    o  The new OH header Time to Live field 

> SHOULD
MUST
>  be copied from the
>       stripped OH header Time to Live field.
>
>    o  The new OH header Type of Service field SHOULD be copied from the
>       stripped OH header Type of Service field (with one caveat, see
>       below)..
>
>    Copying the TTL serves two purposes: first, it preserves the distance
>    the host intended the packet to travel; second, and more importantly,
>    it provides for suppression of looping packets in the event there is
>    a loop of concatenated tunnels due to misconfiguration.
>
>    When
>
>    *The ECN field occupies bits 6 and 7 of both* the *IPv4* Type of Service code-points indicate
>    *field and* the use *IPv6 Traffic Class field [RFC3168].  The ECN field
>    requires special treatment in order to avoid discarding indications*
>    of *congestion [RFC3168].  ITR encapsulation MUST copy the 2-bit* ECN
>    according
>    *field from the inner header* to [RFC3168], the full-functionality option for simple
>    tunnels will be used when ITR encapsulating and *outer header.  Re-encapsulation
>    MUST copy the 2-bit ECN field from the stripped outer header to the
>    new outer header.  If the ECN field contains a congestion indication
>    codepoint (the value is '11', the Congestion Experienced (CE)
>    codepoint), then* ETR decapsulating.
>    Therefore, *decapsulation MUST copy the 2-bit ECN field from
>    the stripped outer header to the surviving inner header that is used
>    to forward the packet beyond* the *ETR.  These requirements preserve*
>    Congestion Experience *Experienced* (CE) bit will be preserved *indications* when a packet traveres *that uses ECN
>    traverses* a LISP tunnel.
>
> 5.4.  Dealing *tunnel and becomes marked* with Large Encapsulated Packets
>
>    In the *a CE indication due
>    to congestion between the tunnel endpoints.
>
> 5.4.  Dealing with Large Encapsulated Packets
>
>    In the* event that the MTU issues mentioned above prove to be more
>    serious than expected, this section proposes 2 simple mechanisms to
>    deal with large packets.  One is stateless using IP fragmentation and
>    the other is stateful using Path MTU Discovery [RFC1191].
>
>    It is left to the implementor to decide if the stateless or stateful
>    mechanism should be implemented.  Both or neither can be decided as
>    well since it is a local decision in the ITR regarding how to deal
>    with MTU issues.  Sites can interoperate with differing mechanisms.
>
> 5.4.1.  A Stateless Solution to MTU Handling
>
>    An ITR stateless solution to handle MTU issues is described as
>    follows:
>
>    1.  Define an architectural constant S for the maximum size of a
>        packet, in bytes, an ITR would receive from a source inside of
>        its site.
>
>    2.  Define L to be the maximum size, in bytes, a packet of size S
>        would be after the ITR prepends the LISP header, UDP header, and
>        outer network layer header of size H.
>
>    3.  Calculate: S + H = L.
>
>    When an ITR receives a packet from a site-facing interface and adds H
>    bytes worth of encapsulation to yield a packet size of L bytes, it
>    resolves the MTU issue by first splitting the original packet into 2
>    equal-sized fragments.  A LISP header is then prepended to each
>    fragment.  This will ensure that the new, encapsulated packets are of
>    size (S/2 + H), which is always below the effective tunnel MTU.
>
>    When an ETR receives encapsulated fragments, it treats them as two
>    individually encapsulated packets.  It strips the LISP headers then
>    forwards each fragment to the destination host of the destination
>    site.  The two fragments are reassembled at the destination host into
>    the single IP datagram that was originated by the source host.
>
>    This behavior is performed by the ITR when the source host originates
>    a packet with the DF field of the IP header is set to 0.  When the DF
>    field of the IP header is set to 1, or the packet is an IPv6 packet
>    originated by the source host, the ITR will drop the packet when the
>    size is greater than L, and sends an ICMP Too Big message to the
>    source with a value of S, where S is (L - H).
>
>    When the outer header encapsulation uses an IPv4 header the DF bit is
>    always set to 0.
>
>    This specification recommends that L be defined as 1500.
>
> 5.4.2.  A Stateful Solution to MTU Handling
>
>    An ITR stateful solution to handle MTU issues is describe as follows
>    and was first introduced in [OPENLISP]:
>
>    1.  The ITR will keep state of the effective MTU for each locator per
>        mapping cache entry.  The effective MTU is what the core network
>        can deliver along the path between ITR and ETR.
>
>    2.  When an encapsulated packet, with DF bit always set to 0, exceeds
>        what the core network can deliver, one of the intermediate
>        routers on the path will send an ICMP Too Big message to the ITR.
>   
Too Big is v6 only, in v4, it is a type 3, code 4 (Frag needed). It 
makes no sense to send ICMPv6 if in v4. It is a mistake we did in the 
OpenLISP implem report.
>        The ITR will parse the ICMP message to determine which locator is
>        affected by the effective MTU change and then record the new
>        effective MTU value in the mapping cache entry.
>
>    3.  When a packet is received by the ITR from a source inside of the
>        site and the size of the packet is greater than the effective MTU
>        stored with the mapping cache entry associated with the
>        destination EID the packet is for, the ITR will send an ICMP Too
>        Big message back to the source.  The packet size advertised by
>        the ITR in the ICMP Too Big message is the effective MTU minus
>        the LISP encapsulation length.
>
>    Even though this mechanism is stateful, it has advantages over the
>    stateless IP fragmentation mechanism, by not involving the
>    destination host with reassembly of ITR fragmented packets.
>
> 6.  EID-to-RLOC Mapping
>
> 6.1.  LISP IPv4 and IPv6 Control Plane Packet Formats
>
>    The following new UDP packet types are used to retrieve EID-to-RLOC
>    mappings:
>
>        0                   1                   2                   3
>        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |Version|  IHL  |Type of Service|          Total Length         |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |         Identification        |Flags|      Fragment Offset    |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |  Time to Live | Protocol = 17 |         Header Checksum       |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                    Source Routing Locator                     |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                 Destination Routing Locator                   |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |           Source Port         |         Dest Port             |
>    UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      \ |           UDP Length          |        UDP Checksum           |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                                                               |
>        |                         LISP Message                          |
>        |                                                               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>         0                   1                   2                   3
>         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |Version| Traffic Class |           Flow Label                  |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |         Payload Length        | Next Header=17|   Hop Limit   |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                                                               |
>        +                                                               +
>        |                                                               |
>        +                     Source Routing Locator                    +
>        |                                                               |
>        +                                                               +
>        |                                                               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                                                               |
>        +                                                               +
>        |                                                               |
>        +                  Destination Routing Locator                  +
>        |                                                               |
>        +                                                               +
>        |                                                               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |           Source Port         |         Dest Port             |
>    UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      \ |           UDP Length          |        UDP Checksum           |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                                                               |
>        |                         LISP Message                          |
>        |                                                               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>    The LISP UDP-based messages are the Map-Request and Map-Reply
>    messages.  When a UDP Map-Request is sent, the UDP source port is
>    chosen by the sender and the destination UDP port number is set to
>    4342.  When a UDP Map-Reply is sent, the source UDP port number is
>    set to 4342 and the destination UDP port number is copied from the
>    source port of either the Map-Request or the invoking data packet.
>
>   
Could we simplify by:

   The LISP UDP-based messages are the Map-Request and Map-Reply
   messages.  When a UDP Map-Request is sent, the UDP source port
   SHOULD be 4342 and the destination UDP port number is set to
   4342.  When a UDP Map-Reply is sent, the source UDP port number is
   set to 4342 and the destination UDP port number is copied from the
   source port of either the Map-Request or the invoking data packet.


It makes the source able to chose the port be, in practice, a default 
value of 4342 is used. I think that only few site require a non-4342 
source and, because dest cannot be chosen, all the site are forced to 
listen 4342...
>    The UDP Length field will reflect the length of the UDP header and
>    the LISP Message payload.
>
>    The UDP Checksum is computed and set to non-zero for Map-Request and
>    Map-Reply messages.  It MUST be checked on receipt and if the
>    checksum fails, the packet MUST be dropped.
>
>    LISP-CONS [CONS] use TCP to send LISP control messages.  The format
>    of control messages includes the UDP header so the checksum and
>    length fields can be used to protect and delimit message boundaries.
>
>    This main LISP specification is the authoritative source for message
>    format definitions for the Map-Request and Map-Reply messages.
>
> 6.1.1.  LISP Packet Type Allocations
>
>    This section will be the authoritative source for allocating LISP
>    Type values.  Current allocations are:
>
>        Reserved:                        0    b'0000'
>        LISP Map-Request:                1    b'0001'
>        LISP Map-Reply:                  2    b'0010'
>        LISP Map-Register:               3    b'0011'
>   

>        LISP-CONS Open Message:          8    b'1000'
>        LISP-CONS Push-Add Message:      9    b'1001'
>        LISP-CONS Push-Delete Message:   10   b'1010'
>        LISP-CONS Unreachable Message    11   b'1011'
>
>   
Remove, cons is not consider in the WG.
> 6.1.2.  Map-Request Message Format
>
>         0                   1                   2                   3
>         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |S|
>        *|*                       Locator Reach Bits                      |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                             Nonce                             |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |Type=1 |A|R| *|A|R|P|S|*         Reserved              | Record Count  |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |         Source-EID-AFI        |            ITR-AFI            |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                   Source EID Address  ...                     |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                Originating ITR RLOC Address ...               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      / |   Reserved    | EID mask-len  |        EID-prefix-AFI         |
>    Rec +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      \ |                       EID-prefix  ...                         |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                   Map-Reply Record  ...                       |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                     Mapping Protocol Data                     |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>    Packet field descriptions:
>
>    S: This is the SMR bit.  See Section 6.5.2 for details.
>
>   

>    Locator Reach Bits:  These bits MUST be set to 0 on transmission and
>       ignored on receipt.  They cannot be used for indicating
>       reachability because the Map-Request does not have the EID-prefix
>       for the sending site so the receiver of the Map-Request cannot
>       know what mapping entry to associate the reachability with.
>       However, when Mapping Data is provided in the Map-Reply Record
>       field, and the receiver of the Map-Request is configured to accept
>       the mapping data, the R-bit per locator entry in the EID-prefix
>       record is used to denote reachability.
>
>   
if no use, remove them!
>    Nonce:  A 4-byte random value created by the sender of the Map-
>       Request.
>   
3-bytes to be consistent with the data-plane. Or give another name.
>    Type:   1 (Map-Request)
>
>    A: This is an authoritative bit, which is set to 0 for UDP-based Map-
>       Requests sent by an ITR.  See other control-specific documents
>       [CONS] for TCP-based Map-Requests.
>
>    R: When set, it indicates a Map-Reply Record segment is included in
>       the Map-Request.
>
>   

>    *P: Indicates that a Map-Request should be treated as a "piggyback"
>       locator reachability probe.  The receiver should respond with a
>       Map-Reply with the P bit set and the nonce copied from the Map-
>       Request.  Details on this usage will be provided in a future
>       version of this draft.
>
> *
If you do not explain what it is, do not put it in the draft yet. 
Please, specify before implementing, otherwise, it is very difficult to 
make OpenLISP compatible with what you do. This is the role of "reserved 
flags"...
> *   S: This is the SMR bit.  See Section 6.5.2 for details.*
>
>    Reserved:  Set to 0 on transmission and ignored on receipt.
>
>    Record Count:  The number of records in this request message.  A
>       record is comprised of the portion of the packet is labeled 'Rec'
>       above and occurs the number of times equal to Record count.
>
>    Source-EID-AFI:  Address family of the "Source EID Address" field.
>
>    ITR-AFI:  Address family of the "Originating ITR RLOC Address" field.
>
>    Source EID Address:  This is the EID of the source host which
>       originated the packet which is invoking this Map-Request.
>
>    Originating ITR RLOC Address:  Used to give the ETR the option of
>       returning a Map-Reply in the address-family of this locator.
>
>    EID mask-len:  Mask length for EID prefix.
>
>    EID-AFI:  Address family of EID-prefix according to [RFC2434]
>
>    EID-prefix:  4 bytes if an IPv4 address-family, 16 bytes if an IPv6
>       address-family.  When a Map-Request is sent by an ITR because a
>       data packet is received for a destination where there is no
>       mapping entry, the EID-prefix is set to the destination IP address
>       of the data packet.  And the 'EID mask-len' is set to 32 or 128
>       for IPv4 or IPv6, respectively.  When an xTR wants to query a site
>       about the status of a mapping it already has cached, the EID-
>       prefix used in the Map-Request has the same mask-length as the
>       EID-prefix returned from the site when it sent a Map-Reply
>       message.
>
>    Map-Reply Record:  When the R bit is set, this field is the size of
>       the "Record" field in the Map-Reply format.  This Map-Reply record
>       contains the EID-to-RLOC mapping entry associated with the Source
>       EID.  This allows the ETR which will receive this Map-Request to
>       cache the data if it chooses to do so.
>
>    Mapping Protocol Data:  See [CONS] or [ALT] for details.  This field
>       is optional and present when the UDP length indicates there is
>       enough space in the packet to include it.
>
> 6.1.3.  EID-to-RLOC UDP Map-Request Message
>
>    A Map-Request is sent from an ITR when it needs a mapping for an EID,
>    wants to test an RLOC for reachability,
you thus consider control and data plane paths being the same?
>  or wants to refresh a mapping
>    before TTL expiration.  For the initial case, the destination IP
>    address used for the Map-Request is the destination-EID from the
>    packet which had a mapping cache lookup failure.  For the later 2
>    cases, the destination IP address used for the Map-Request is one of
>    the RLOC addresses from the locator-set of the map cache entry.  In
>    all cases, the UDP source port number for the Map-Request message is
>    a randomly allocated 16-bit value and the UDP destination port number
>    is set to the well-known destination port number 4342.  A successful
>    Map-Reply updates the cached set of RLOCs associated with the EID
>    prefix range.
>
>    Map-Requests can also be LISP encapsulated using UDP destination port
>    4341 when sent from an ITR to a Map-Resolver.  Likewise, Map-Requests
>    are LISP encapsulated the same way from a Map-Server to an ETR.
>    Details on encapsulated Map-Requests and Map-Resolvers can be found
>    in [LISP-MS].
>
>    Map-Requests MUST be rate-limited.  It is recommended that a Map-
>    Request for the same EID-prefix be sent no more than once per second.
>   
Why 1 second? As the TTL is with a one minute granularity, why 1 
second?  for when TTL is set to 0? If it is for the SMR bit, this bit 
should not be seen too frequently, otherwise, the 1minute granularity 
TTL has to be revised.
> 6.1.4.  Map-Reply Message Format
>
>         0                   1                   2                   3
>         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |x|
>        *|*                       Locator Reach Bits                      |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                             Nonce                             |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |Type=2 | *|P|*            Reserved                 | Record Count  |
>    +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |   |                          Record  TTL                          |
>    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    R   | Locator Count | EID mask-len  |A| ACT |  Reserved             |
>    e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    c   |           Reserved            |            EID-AFI            |
>    o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    r   |                          EID-prefix                           |
>    d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
>    | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    | o |           Unused Flags      |R|           Loc-AFI             |
>    | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |  \|                             Locator                           |
>    +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                     Mapping Protocol Data                     |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>    Packet field descriptions:
>
>    x: Set to 0 on transmission and ignored on receipt.
>
>   

>    Locator Reach Bits:  Refer to Section 5.3.  This field MUST be set to
>       0 on transmission and ignored on receipt.  The locator
>       reachability is encoded as the R-bit in each locator entry of each
>       EID-prefix record.
>
>   
Not used, then remove it.
>    Nonce:  A 4-byte value set in a Data-Probe packet or a Map-Request
>       that is echoed here in the Map-Reply.
>
>   
3-bytes or change the name.
>    Type:   2 (Map-Reply)
>
>    *P: Indicates that the Map-Reply is in response to a "piggyback"
>       locator reachability Map-Request.  The nonce field should contain
>       a copy of the nonce value from the original Map-Request.  Details
>       on this usage will be provided in a future version of this draft.*
>
>   
cf supra (remove this part or explain it)
>    Reserved:  Set to 0 on transmission and ignored on receipt.
>
>    Record Count:  The number of records in this reply message.  A record
>       is comprised of that portion of the packet labeled 'Record' above
>       and occurs the number of times equal to Record count.
>
>    Record TTL:  The time in minutes the recipient of the Map-Reply will
>       store the mapping.  If the TTL is 0, the entry should be removed
>       from the cache immediately.  If the value is 0xffffffff, the
>       recipient can decide locally how long to store the mapping.
>
>   
32-bit for one minute granularity TTL means that a mapping can live 8171 
years, reduce the side to win space or switch to a one second 
granularity (136 years should be enough ;-) ) (but you can recommend to 
use > 1minute TTL).
>    Locator Count:  The number of Locator entries.  A locator entry
>       comprises what is labeled above as 'Loc'.  The locator count can
>       be 0 indicating there are no locators for the EID-prefix.
>
>    EID mask-len:  Mask length for EID prefix.
>
>    A: The Authoritative bit, when sent by a UDP-based message is always
>       set by the ETR.

> See [CONS] for TCP-based Map-Replies.
>
>   
remove as CONS is not considered.
>    ACT:  This 3-bit field describes negative Map-Reply actions.  These
>       bits are used only when the 'Locator Count' field is set to 0.
>       The action bits are encoded only in Map-Reply messages.  The
>       actions defined are used by an ITR or PTR when a destination EID
>       matches a negative mapping cache entry.  The current assigned
>       values are:
>
>       (0) No action:  No action is being conveyed by the sender of the
>          Map-Reply message.
>
>       (1) Natively-Forward:  The packet is not encapsulated or dropped
>          but natively forwarded.
>
>       (2) Drop:  The packet is dropped silently.
>
>       (3) Send-Map-Request:  The packet invokes sending a Map-Request.
>
>    EID-AFI:  Address family of EID-prefix according to [RFC2434].
>
>    EID-prefix:  4 bytes if an IPv4 address-family, 16 bytes if an IPv6
>       address-family.
>
>    Priority:  each RLOC is assigned a unicast priority.  Lower values
>       are more preferable.  When multiple RLOCs have the same priority,
>       they may be used in a load-split fashion.  A value of 255 means
>       the RLOC MUST NOT be used for unicast forwarding.
>
>    Weight:  when priorities are the same for multiple RLOCs, the weight
>       indicates how to balance unicast traffic between them.  Weight is
>       encoded as a percentage of total unicast packets that match the
>       mapping entry.  If a non-zero weight value is used for any RLOC,
>       then all RLOCs must use a non-zero weight value and then the sum
>       of all weight values MUST equal 100.  If a zero value is used for
>       any RLOC weight, then all weights MUST be zero and the receiver of
>       the Map-Reply will decide how to load-split traffic.  See
>       Section 6.4 for a suggested hash algorithm to distribute load
>       across locators with same priority and equal weight values.  When
>       a single RLOC exists in a mapping entry, the weight value MUST be
>       set to 100 and ignored on receipt.
>
>    M Priority:  each RLOC is assigned a multicast priority used by an
>       ETR in a receiver multicast site to select an ITR in a source
>       multicast site for building multicast distribution trees.  A value
>       of 255 means the RLOC MUST NOT be used for joining a multicast
>       distribution tree.
>
>    M Weight:  when priorities are the same for multiple RLOCs, the
>       weight indicates how to balance building multicast distribution
>       trees across multiple ITRs.  The weight is encoded as a percentage
>       of total number of trees build to the source site identified by
>       the EID-prefix.  If a non-zero weight value is used for any RLOC,
>       then all RLOCs must use a non-zero weight value and then the sum
>       of all weight values MUST equal 100.  If a zero value is used for
>       any RLOC weight, then all weights MUST be zero and the receiver of
>       the Map-Reply will decide how to distribute multicast state across
>       ITRs.
>
>    Unused Flags:  set to 0 when sending and ignored on receipt.
>
>    R: when this bit is set, the locator is known to be reachable from
>       the Map-Reply sender's perspective.  When there is a single
>       mapping record in the message, the R-bit for each locator must
>       have a consistent setting with the bitfield setting of the 'Loc
>       Reach Bits' field in the early part of the header.  When there are
>       multiple mapping records in the message, the 'Loc Reach Bits'
>       field is set to 0.
>
>    Locator:  an IPv4 or IPv6 address (as encoded by the 'Loc-AFI' field)
>       assigned to an ETR or router acting as a proxy replier for the
>       EID-prefix.  Note that the destination RLOC address MAY be an
>       anycast address.  A source RLOC can be an anycast address as well.
>       The source or destination RLOC MUST NOT be the broadcast address
>       (255.255.255.255 or any subnet broadcast address known to the
>       router), and MUST NOT be a link-local multicast address.  The
>       source RLOC MUST NOT be a multicast address.  The destination RLOC
>       SHOULD be a multicast address if it is being mapped from a
>       multicast destination EID.
>
>    Mapping Protocol Data:  See [CONS] or [ALT] for details.  This field
>       is optional and present when the UDP length indicates there is
>       enough space in the packet to include it.
>
> 6.1.5.  EID-to-RLOC UDP Map-Reply Message
>
>    When a Data Probe packet or a Map-Request triggers a Map-Reply to be
>    sent, the RLOCs associated with the EID-prefix matched by the EID in
>    the original packet destination IP address field will be returned.
>    The RLOCs in the Map-Reply are the globally-routable IP addresses of
>    the ETR but are not necessarily reachable; separate testing of
>    reachability is required.
>
>    Note that a Map-Reply may contain different EID-prefix granularity
>    (prefix + length) than the Map-Request which triggers it.  This might
>    occur if a Map-Request were for a prefix that had been returned by an
>    earlier Map-Reply.  In such a case, the requester updates its cache
>    with the new prefix information and granularity.  For example, a
>    requester with two cached EID-prefixes that are covered by a Map-
>    Reply containing one, less-specific prefix, replaces the entry with
>    the less-specific EID-prefix.  Note that the reverse, replacement of
>    one less-specific prefix with multiple more-specific prefixes, can
>    also occur but not by removing the less-specific prefix rather by
>    adding the more-specific prefixes which during a lookup will override
>    the less-specific prefix.
>
>    Replies SHOULD be sent for an EID-prefix no more often than once per
>    second to the same requesting router.  For scalability, it is
>    expected that aggregation of EID addresses into EID-prefixes will
>    allow one Map-Reply to satisfy a mapping for the EID addresses in the
>    prefix range thereby reducing the number of Map-Request messages.
>
>    The addresses for a encapsulated data packets or Map-Request message
>    are swapped and used for sending the Map-Reply.  The UDP source and
>    destination ports are swapped as well.  That is, the source port in
>    the UDP header for the Map-Reply is set to the well-known UDP port
>    number 4342.
>
>    Map-Reply records can have an empty locator-set.  This type of a Map-
>    Reply is called a Negative Map-Reply.  Negative Map-Replies convey
>    special actions by the sender to the ITR or PTR which have solicited
>    the Map-Reply.  There are two primary applications for Negative Map-
>    Replies.  The first is for a Map-Resolver to instruct an ITR or PTR
>    when a destination is for a LISP site versus a non-LISP site.  And
>    the other is to source quench Map-Requests which are sent for non-
>    allocated EIDs.
>
> 6.1.6.  Map-Register Message Format
>
>    The usage details of the Map-Register message can be found in
>    specification [LISP-MS].  This section solely defines the message
>    format.
>
>    The message is sent in a UDP with a destination UDP port 4342 and a
>    randomly selected UDP port number.  Before an IPv4 or IPv6 network
>    layer header is prepended, an AH header is prepended to carry
>    authentication information.  The format conforms to the IPsec
>    specification [RFC2402].  The Map-Register message will use transport
>    mode by setting the IP protocol number field or the IPv6 next-header
>    field to 51.
>
>    The AH header from [RFC2402] is:
>
>         0                   1                   2                   3
>         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        | Next Header   |  Payload Len  |          RESERVED             |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                 Security Parameters Index (SPI)               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                    Sequence Number Field                      |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                                                               |
>        +                Authentication Data (variable)                 |
>        |                                                               |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>    The Next Header field is set to UDP.  The SPI field is set to 0
>    (since no Security Association or Key Exchange protocol is being
>    used).  The Sequence Number is a randomly chosen value by the sender.
>    The Authentication Data is 16 bytes and holds a MD5 HMAC.
>
>    The Map-Register message format is:
>
>         0                   1                   2                   3
>         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |x|
>        *|*                       Locator Reach Bits                      |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |                             Nonce                             |
>        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |Type=3 |P|            Reserved                 | Record Count  |
>    +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |   |                          Record  TTL                          |
>    |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    R   | Locator Count | EID mask-len  |A| ACT |  Reserved             |
>    e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    c   |           Reserved            |            EID-AFI            |
>    o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    r   |                          EID-prefix                           |
>    d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
>    | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    | o |           Unused Flags      |R|           Loc-AFI             |
>    | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    |  \|                             Locator                           |
>    +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>    Packet field descriptions:
>
>    x: Set to 0 on transmission and ignored on receipt.
>
>    Locator Reach Bits:  Refer to Section 5.3.  This field MUST be set to
>       0 on transmission and ignored on receipt.  The locator
>       reachability is encoded as the R-bit in each locator entry of each
>       EID-prefix record.
>
>    Nonce:  The Nonce field is set to 0 in Map-Register messages.
>
>    Type:   3 (Map-Register)
>
>    P: This is the Proxy-Map-Reply bit.  When set *Set* to 1, the *1 by an* ETR sending *which sends* a Map-Register is asking *message requesting
>       for* the Map-Server to *proxy Map-Reply.  The Map-Server will* send
>       non-authoritative Map-Replies on behalf of the ETR.  *Details on
>       this usage will be provided in a future version of this draft.*
>
>    Reserved:  Set to 0 on transmission and ignored on receipt.
>
>    Record Count:  The number of records in this Map-Register message.  A
>       record is comprised of that portion of the packet labeled 'Record'
>       above and occurs the number of times equal to Record count.
>
>    The definition of the rest of the Map-Register can be found in the
>    Map-Reply section.
>
> 6.2.  Routing Locator Selection
>
>    Both client-side and server-side may need control over the selection
>    of RLOCs for conversations between them.  This control is achieved by
>    manipulating the Priority and Weight fields in EID-to-RLOC Map-Reply
>    messages.  Alternatively, RLOC information may be gleaned from
>    received tunneled packets or EID-to-RLOC Map-Request messages.
>
>    The following enumerates different scenarios for choosing RLOCs and
>    the controls that are available:
>
>    o  Server-side returns one RLOC.  Client-side can only use one RLOC.
>       Server-side has complete control of the selection.
>
>    o  Server-side returns a list of RLOC where a subset of the list has
>       the same best priority.  Client can only use the subset list
>       according to the weighting assigned by the server-side.  In this
>       case, the server-side controls both the subset list and load-
>       splitting across its members.  The client-side can use RLOCs
>       outside of the subset list if it determines that the subset list
>       is unreachable (unless RLOCs are set to a Priority of 255).  Some
>       sharing of control exists: the server-side determines the
>       destination RLOC list and load distribution while the client-side
>       has the option of using alternatives to this list if RLOCs in the
>       list are unreachable.
>
>    o  Server-side sets weight of 0 for the RLOC subset list.  In this
>       case, the client-side can choose how the traffic load is spread
>       across the subset list.  Control is shared by the server-side
>       determining the list and the client determining load distribution.
>       Again, the client can use alternative RLOCs if the server-provided
>       list of RLOCs are unreachable.
>
>    o  Either side (more likely on the server-side ETR) decides not to
>       send a Map-Request.  For example, if the server-side ETR does not
>       send Map-Requests, it gleans RLOCs from the client-side ITR,
>       giving the client-side ITR responsibility for bidirectional RLOC
>       reachability and preferability.  Server-side ETR gleaning of the
>       client-side ITR RLOC is done by caching the inner header source
>       EID and the outer header source RLOC of received packets.  The
>       client-side ITR controls how traffic is returned and can alternate
>       using an outer header source RLOC, which then can be added to the
>       list the server-side ETR uses to return traffic.  Since no
>       Priority or Weights are provided using this method, the server-
>       side ETR must assume each client-side ITR RLOC uses the same best
>       Priority with a Weight of zero.  In addition, since EID-prefix
>       encoding cannot be conveyed in data packets, the EID-to-RLOC cache
>       on tunnel routers can grow to be very large.
>
>    RLOCs that appear in EID-to-RLOC Map-Reply messages are considered
>    reachable.  The Map-Reply and the database mapping service does not
>    provide any reachability status for Locators.  This is done outside
>    of the mapping service.  See next section for details.
>
> 6.3.  Routing Locator Reachability
>
>    There are 4 methods for determining when a Locator is either
>    reachable or has become unreachable:
>
>    1.  Locator reachability is determined by an ETR by examining the
>        Loc-Reach-Bits from a LISP header of a encapsulated data packet
>        which is provided by an ITR when an ITR encapsulates data.
>
>    2.  Locator unreachability is determined by an ITR by receiving ICMP
>        Network or Host Unreachable messages.
>
>    3.  Locator unreachability can also be determined by an BGP-enabled
>        ITR when there is no prefix matching a Locator address from the
>        BGP RIB.
>
>    4.  Locator unreachability is determined when a host sends an ICMP
>        Port Unreachable message.  This occurs when an ITR may not use
>        any methods of interworking. one which is describe in [INTERWORK]
>        and the encapsulated data packet is received by a host at the
>        destination non-LISP site.
>
>    5.  Locator reachability is determined by receiving a Map-Reply
>        message from a ETR's Locator address in response to a previously
>        sent Map-Request.
>
>    6.  Locator reachability can also be determined by receiving packets
>        encapsulated by the ITR assigned to the locator address.
>
>    When determining Locator reachability by examining the Loc-Reach-Bits
>    from the LISP encapsulate data packet, an ETR will receive up to date
>    status from the ITR closest to the Locators at the source site.  The
>    ITRs at the source site can determine reachability when running their
>    IGP at the site.  When the ITRs are deployed on CE routers, typically
>    a default route is injected into the site's IGP from each of the
>    ITRs.  If an ITR goes down, the CE-PE link goes down, or the PE
>    router goes down, the CE router withdraws the default route.  This
>    allows the other ITRs at the site to determine one of the Locators
>    has gone unreachable.
>
>    The Locators listed in a Map-Reply are numbered with ordinals 0 to
>    n-1.  The Loc-Reach-Bits in a LISP Data Message are numbered from 0
>    to n-1 starting with the least significant bit numbered as 0.  So,
>    for example, if the ITR with locator listed as the 3rd Locator
>    position in the Map-Reply goes down, all other ITRs at the site will
>    have the 3rd bit from the right cleared (the bit that corresponds to
>    ordinal 2).
>
>    When an ETR decapsulates a packet, it will look for a change in the
>    Loc-Reach-Bits value.  When a bit goes from 1 to 0, the ETR will
>    refrain from encapsulating packets to the Locator that has just gone
>    unreachable.  It can start using the Locator again when the bit that
>    corresponds to the Locator goes from 0 to 1.  Loc-Reach-Bits are
>    associated with a locator-set per EID-prefix.  Therefore, when a
>    locator becomes unreachable, the loc-reach-bit that corresponds to
>    that locator's position in the list returned by the last Map-Reply
>    will be set to zero for that particular EID-prefix.
>
>    When ITRs at the site are not deployed in CE routers, the IGP can
>    still be used to determine the reachability of Locators provided they
>    are injected a stub links into the IGP.  This is typically done when
>    a /32 address is configured on a loopback interface.
>
>    When ITRs receive ICMP Network or Host Unreachable messages as a
>    method to determine unreachability, they will refrain from using
>    Locators which are described in Locator lists of Map-Replies.
>    However, using this approach is unreliable because many network
>    operators turn off generation of ICMP Unreachable messages.
>
>    If an ITR does receive an ICMP Network or Host Unreachable message,
>    it MAY originate its own ICMP Unreachable message destined for the
>    host that originated the data packet the ITR encapsulated.
>
>    Also, BGP-enabled ITRs can unilaterally examine the BGP RIB to see if
>    a locator address from a locator-set in a mapping entry matches a
>    prefix.  If it does not find one and BGP is running in the Default
>    Free Zone (DFZ), it can decide to not use the locator even though the
>    Loc-Reach-Bits indicate the locator is up.  In this case, the path
>    from the ITR to the ETR that is assigned the locator is not
>    available.  More details are in [LOC-ID-ARCH].
>
>    Optionally, an ITR can send a Map-Request to a Locator and if a Map-
>    Reply is returned, reachability of the Locator has been determined.
>    Obviously, sending such probes increases the number of control
>    messages originated by tunnel routers for active flows, so Locators
>    are assumed to be reachable when they are advertised.
>
>    This assumption does create a dependency: Locator unreachability is
>    detected by the receipt of ICMP Host Unreachable messages.  When an
>    Locator has been determined to be unreachable, it is not used for
>    active traffic; this is the same as if it were listed in a Map-Reply
>    with priority 255.
>
>    The ITR can test the reachability of the unreachable Locator by
>    sending periodic Requests.  Both Requests and Replies MUST be rate-
>    limited.  Locator reachability testing is never done with data
>    packets since that increases the risk of packet loss for end-to-end
>    sessions.
>
>    When an ETR is decapsulating packets, *decapsulates a packet,* it can be sure *knows* that the path *it is reachable* from
>    the encapsulating ITR *because that* is available.  The *how the packet arrived.  In
>    most cases, the* ETR can *also reach the ITR but cannot* assume *this to
>    be true due to* the *possibility of* path
>    from *assymetry.  In* the ETR *presence of
>    unidirectional traffic flow from an ITR* to *an ETR,* the ITR *should not
>    use the lack of return traffic as an indication that the ETR* is also reachable.  Even if
>    *unreachable.  Instead, it must use an alternate mechanisms to
>    determine reachability.
>
> 6.3.1.  Echo Nonce Algorithm
>
> *
To clarify this section, it should be rewritten with the idea that this 
is a hint for the "non-reachability". If the reply comes, perfect, we 
have reachability. Otherwise, it is a hint that there is maybe a 
reachability issue and then another technique has to be used.

Regards

Damien Saucez

> *   When* there is
>    asymmetric routing *bidirectional data flow between a pair of locators, a
>    simple mechanism called "nonce echoing" can be used to determine
>    reachability between an ITR and ETR.  When an ITR wants to solicit a
>    nonce echo, it sets the E-bit and places a 24-bit nonce* in the core, *LISP
>    header of* the first-hop *next encapsulated data packet.
>
>    When this packet is received by the ETR, the encapsulated packet is
>    forwarded as normal.  When the ETR next sends a data packet to the
>    ITR, it includes the nonce received earlier.  The ITR sees this "echo
>    nonce reply"* and last-hop ASes will
>    be *knows* the same *path to and from the ETR is up.
>
>    The time the ITR waits* for both directions of traffic since the *echoed nonce before it determines the
>    path is down is variable and a choice left for the implementation.
>
>    If the ITR is receiving packets from the ETR but does not see the
>    nonce echoed, then the path to the ETR is down.  This decision may be
>    overridden by other* locator
>    addresses *reachability algorithms.  Once the ITR
>    determines the path to the ETR is down it can switch to another
>    locator for that EID-prefix.
>
>    Note that "ITR" and "ETR"* are out of *relative terms here.  Both devices must
>    be implementing both ITR and ETR functionality for* the PA blocks *echo nonce
>    mechanism to operate.
>
>    The ITR and ETR may both go into echo-nonce-request state at the same
>    time.  The number* of each. *packets sent or the time during which echo nonce
>    requests are sent is an implementation specific setting.*  However,
>    *when an ITR is in echo-nonce-request state, it can echo the ETR's
>    nonce in the next packet that it encapsulates and then subsequently,
>    continue sending echo-nonce-request packets.
>
>    This mechanism does not completely solve the forward path
>    reachability problem as traffic may be unidirectional.  That is,* the assumption
>    *ETR receiving traffic at a site may not* may not always be valid, so this mechanism should be used as a best-
>    effort indication that a working path exists between the sites.  In the event of unidirectional traffic from *same device as*
>    an ITR *which transmits traffic from that site or the site* to an ETR, an *site
>    traffic is unidirectional so there is no* ITR
>    should not conclude *returning traffic.
>
>    Note* that a *other* locator is unreachable since it is not
>    receiving packets, but use alternate *reachability* mechanisms described above to
>    determine reachability. *are being researched.*
>
> 6.4.  Routing Locator Hashing
>
>    When an ETR provides an EID-to-RLOC mapping in a Map-Reply message to
>    a requesting ITR, the locator-set for the EID-prefix may contain
>    different priority values for each locator address.  When more than
>    one best priority locator exists, the ITR can decide how to load
>    share traffic against the corresponding locators.
>
>    The following hash algorithm may be used by an ITR to select a
>    locator for a packet destined to an EID for the EID-to-RLOC mapping:
>
>    1.  Either a source and destination address hash can be used or the
>        traditional 5-tuple hash which includes the source and
>        destination addresses, source and destination TCP, UDP, or SCTP
>        port numbers and the IP protocol number field or IPv6 next-
>        protocol fields of a packet a host originates from within a LISP
>        site.  When a packet is not a TCP, UDP, or SCTP packet, the
>        source and destination addresses only from the header are used to
>        compute the hash.
>
>    2.  Take the hash value and divide it by the number of locators
>        stored in the locator-set for the EID-to-RLOC mapping.
>
>    3.  The remainder will be yield a value of 0 to "number of locators
>        minus 1".  Use the remainder to select the locator in the
>        locator-set.
>
>    Note that when a packet is LISP encapsulated, the source port number
>    in the outer UDP header needs to be set.  Selecting a random value
>    allows core routers which are attached to Link Aggregation Groups
>    (LAGs) to load-split the encapsulated packets across member links of
>    such LAGs.  Otherwise, core routers would see a single flow, since
>    packets have a source address of the ITR, for packets which are
>    originated by different EIDs at the source site.  A suggested setting
>    for the source port number computed by an ITR is a 5-tuple hash
>    function on the inner header, as described above.
>
> 6.5.  Changing the Contents of EID-to-RLOC Mappings
>
>    Since the LISP architecture uses a caching scheme to retrieve and
>    store EID-to-RLOC mappings, the only way an ITR can get a more up-to-
>    date mapping is to re-request the mapping.  However, the ITRs do not
>    know when the mappings change and the ETRs do not keep track of who
>    requested its mappings.  For scalability reasons, we want to maintain
>    this approach but need to provide a way for ETRs change their
>    mappings and inform the sites that are currently communicating with
>    the ETR site using such mappings.
>
>    When a locator record is added to the end of a locator-set, it is
>    easy to update mappings.  We assume new mappings will maintain the
>    same locator ordering as the old mapping but just have new locators
>    appended to the end of the list.  So some ITRs can have a new mapping
>    while other ITRs have only an old mapping that is used until they
>    time out.  When an ITR has only an old mapping but detects bits set
>    in the loc-reach-bits that correspond to locators beyond the list it
>    has cached, it simply ignores them.
>
>    When a locator record is removed from a locator-set, ITRs that have
>    the mapping cached will not use the removed locator because the xTRs
>    will set the loc-reach-bit to 0.  So even if the locator is in the
>    list, it will not be used.  For new mapping requests, the xTRs can
>    set the locator address to 0 as well as setting the corresponding
>    loc-reach-bit to 0.  This forces ITRs with old or new mappings to
>    avoid using the removed locator.
>
>    If many changes occur to a mapping over a long period of time, one
>    will find empty record slots in the middle of the locator-set and new
>    records appended to the locator-set.  At some point, it would be
>    useful to compact the locator-set so the loc-reach-bit settings can
>    be efficiently packed.
>
>    We propose here two approaches for locator-set compaction, one
>    operational and the other a protocol mechanism.  The operational
>    approach uses a clock sweep method.  The protocol approach uses the
>    concept of Solicit-Map-Requests.
>
> 6.5.1.  Clock Sweep
>
>    The clock sweep approach uses planning in advance and the use of
>    count-down TTLs to time out mappings that have already been cached.
>    The default setting for an EID-to-RLOC mapping TTL is 24 hours.  So
>    there is a 24 hour window to time out old mappings.  The following
>    clock sweep procedure is used:
>
>    1.  24 hours before a mapping change is to take effect, a network
>        administrator configures the ETRs at a site to start the clock
>        sweep window.
>
>    2.  During the clock sweep window, ETRs continue to send Map-Reply
>        messages with the current (unchanged) mapping records.  The TTL
>        for these mappings is set to 1 hour.
>
>    3.  24 hours later, all previous cache entries will have timed out,
>        and any active cache entries will time out within 1 hour.  During
>        this 1 hour window the ETRs continue to send Map-Reply messages
>        with the current (unchanged) mapping records with the TTL set to
>        1 minute.
>
>    4.  At the end of the 1 hour window, the ETRs will send Map-Reply
>        messages with the new (changed) mapping records.  So any active
>        caches can get the new mapping contents right away if not cached,
>        or in 1 minute if they had the mapping cached.
>
> 6.5.2.  Solicit-Map-Request (SMR)
>
>    Soliciting a Map-Request is a selective way for xTRs, at the site
>    where mappings change, to control the rate they receive requests for
>    Map-Reply messages.  SMRs are also used to tell remote ITRs to update
>    the mappings they have cached.
>
>    Since the xTRs don't keep track of remote ITRs that have cached their
>    mappings, they can not tell exactly who needs the new mapping
>    entries.  So an xTR will solicit Map-Requests from sites it is
>    currently sending encapsulated data to, and only from those sites.
>    The xTRs can locally decide the algorithm for how often and to how
>    many sites it sends SMR messages.
>
>    An SMR message is simply a bit set in an encapsulated data packet
>    (and a Map-Request message).  When an ETR at a remote site
>    decapsulates a data packet that has the SMR bit set, it can tell that
>    a new Map-Request message is being solicited.  Both the xTR that
>    sends the SMR message and the site that acts on the SMR message MUST
>    be rate-limited.
>
>    The following procedure shows how a SMR exchange occurs when a site
>    is doing locator-set compaction for an EID-to-RLOC mapping:
>
>    1.  When the database mappings in an ETR change, the ITRs at the site
>        begin to set the SMR bit in packets they encapsulate to the sites
>        they communicate with.
>
>    2.  A remote xTR which decapsulates a packet with the SMR bit set
>        will schedule sending a Map-Request message to the source locator
>        address of the encapsulated packet.  The nonce in the Map-Request
>        is copied from the nonce in the encapsulated data packet that has
>        the SMR bit set.
>
>    3.  The remote xTR retransmits the Map-Request slowly until it gets a
>        Map-Reply while continuing to use the cached mapping.
>
>    4.  The ETRs at the site with the changed mapping will reply to the
>        Map-Request with a Map-Reply message provided the Map-Request
>        nonce matches the nonce from the SMR.  The Map-Reply messages
>        SHOULD be rate limited.  This is important to avoid Map-Reply
>        implosion.
>
>    5.  The ETRs, at the site with the changed mapping, records the fact
>        that the site that sent the Map-Request has received the new
>        mapping data in the mapping cache entry for the remote site so
>        the loc-reach-bits are reflective of the new mapping for packets
>        going to the remote site.  The ETR then stops sending packets
>        with the SMR-bit set.
>
>    For security reasons an ITR MUST NOT process unsolicited Map-Replies.
>    The nonce MUST be carried from SMR packet, into the resultant Map-
>    Request, and then into Map-Reply to reduce spoofing attacks.
>
> 7.  Router Performance Considerations
>
>    LISP is designed to be very hardware-based forwarding friendly.  By
>    doing tunnel header prepending [RFC1955] and stripping instead of re-
>    writing addresses, existing hardware can support the forwarding model
>    with little or no modification.  Where modifications are required,
>    they should be limited to re-programming existing hardware rather
>    than requiring expensive design changes to hard-coded algorithms in
>    silicon.
>
>    A few implementation techniques can be used to incrementally
>    implement LISP:
>
>    o  When a tunnel encapsulated packet is received by an ETR, the outer
>       destination address may not be the address of the router.  This
>       makes it challenging for the control plane to get packets from the
>       hardware.  This may be mitigated by creating special FIB entries
>       for the EID-prefixes of EIDs served by the ETR (those for which
>       the router provides an RLOC translation).  These FIB entries are
>       marked with a flag indicating that control plane processing should
>       be performed.  The forwarding logic of testing for particular IP
>       protocol number value is not necessary.  No changes to existing,
>       deployed hardware should be needed to support this.
>
>    o  On an ITR, prepending a new IP header is as simple as adding more
>       bytes to a MAC rewrite string and prepending the string as part of
>       the outgoing encapsulation procedure.  Many routers that support
>       GRE tunneling [RFC2784] or 6to4 tunneling [RFC3056] can already
>       support this action.
>
>    o  When a received packet's outer destination address contains an EID
>       which is not intended to be forwarded on the routable topology
>       (i.e.  LISP 1.5), the source address of a data packet or the
>       router interface with which the source is associated (the
>       interface from which it was received) can be associated with a VRF
>       (Virtual Routing/Forwarding), in which a different (i.e. non-
>       congruent) topology can be used to find EID-to-RLOC mappings.
>
> 8.  Deployment Scenarios
>
>    This section will explore how and where ITRs and ETRs can be deployed
>    and will discuss the pros and cons of each deployment scenario.
>    There are two basic deployment trade-offs to consider: centralized
>    versus distributed caches and flat, recursive, or re-encapsulating
>    tunneling.
>
>    When deciding on centralized versus distributed caching, the
>    following issues should be considered:
>
>    o  Are the tunnel routers spread out so that the caches are spread
>       across all the memories of each router?
>
>    o  Should management "touch points" be minimized by choosing few
>       tunnel routers, just enough for redundancy?
>
>    o  In general, using more ITRs doesn't increase management load,
>       since caches are built and stored dynamically.  On the other hand,
>       more ETRs does require more management since EID-prefix-to-RLOC
>       mappings need to be explicitly configured.
>
>    When deciding on flat, recursive, or re-encapsulation tunneling, the
>    following issues should be considered:
>
>    o  Flat tunneling implements a single tunnel between source site and
>       destination site.  This generally offers better paths between
>       sources and destinations with a single tunnel path.
>
>    o  Recursive tunneling is when tunneled traffic is again further
>       encapsulated in another tunnel, either to implement VPNs or to
>       perform Traffic Engineering.  When doing VPN-based tunneling, the
>       site has some control since the site is prepending a new tunnel
>       header.  In the case of TE-based tunneling, the site may have
>       control if it is prepending a new tunnel header, but if the site's
>       ISP is doing the TE, then the site has no control.  Recursive
>       tunneling generally will result in suboptimal paths but at the
>       benefit of steering traffic to resource available parts of the
>       network.
>
>    o  The technique of re-encapsulation ensures that packets only
>       require one tunnel header.  So if a packet needs to be rerouted,
>       it is first decapsulated by the ETR and then re-encapsulated with
>       a new tunnel header using a new RLOC.
>
>    The next sub-sections will describe where tunnel routers can reside
>    in the network.
>
> 8.1.  First-hop/Last-hop Tunnel Routers
>
>    By locating tunnel routers close to hosts, the EID-prefix set is at
>    the granularity of an IP subnet.  So at the expense of more EID-
>    prefix-to-RLOC sets for the site, the caches in each tunnel router
>    can remain relatively small.  But caches always depend on the number
>    of non-aggregated EID destination flows active through these tunnel
>    routers.
>
>    With more tunnel routers doing encapsulation, the increase in control
>    traffic grows as well: since the EID-granularity is greater, more
>    Map-Requests and Map-Replies are traveling between more routers.
>
>    The advantage of placing the caches and databases at these stub
>    routers is that the products deployed in this part of the network
>    have better price-memory ratios then their core router counterparts.
>    Memory is typically less expensive in these devices and fewer routes
>    are stored (only IGP routes).  These devices tend to have excess
>    capacity, both for forwarding and routing state.
>
>    LISP functionality can also be deployed in edge switches.  These
>    devices generally have layer-2 ports facing hosts and layer-3 ports
>    facing the Internet.  Spare capacity is also often available in these
>    devices as well.
>
> 8.2.  Border/Edge Tunnel Routers
>
>    Using customer-edge (CE) routers for tunnel endpoints allows the EID
>    space associated with a site to be reachable via a small set of RLOCs
>    assigned to the CE routers for that site.
>
>    This offers the opposite benefit of the first-hop/last-hop tunnel
>    router scenario: the number of mapping entries and network management
>    touch points are reduced, allowing better scaling.
>
>    One disadvantage is that less of the network's resources are used to
>    reach host endpoints thereby centralizing the point-of-failure domain
>    and creating network choke points at the CE router.
>
>    Note that more than one CE router at a site can be configured with
>    the same IP address.  In this case an RLOC is an anycast address.
>    This allows resilience between the CE routers.  That is, if a CE
>    router fails, traffic is automatically routed to the other routers
>    using the same anycast address.  However, this comes with the
>    disadvantage where the site cannot control the entrance point when
>    the anycast route is advertised out from all border routers.
>
> 8.3.  ISP Provider-Edge (PE) Tunnel Routers
>
>    Use of ISP PE routers as tunnel endpoint routers gives an ISP control
>    over the location of the egress tunnel endpoints.  That is, the ISP
>    can decide if the tunnel endpoints are in the destination site (in
>    either CE routers or last-hop routers within a site) or at other PE
>    edges.  The advantage of this case is that two or more tunnel headers
>    can be avoided.  By having the PE be the first router on the path to
>    encapsulate, it can choose a TE path first, and the ETR can
>    decapsulate and re-encapsulate for a tunnel to the destination end
>    site.
>
>    An obvious disadvantage is that the end site has no control over
>    where its packets flow or the RLOCs used.
>
>    As mentioned in earlier sections a combination of these scenarios is
>    possible at the expense of extra packet header overhead, if both site
>    and provider want control, then recursive or re-encapsulating tunnels
>    are used.
>
> 9.  Traceroute Considerations
>
>    When a source host in a LISP site initiates a traceroute to a
>    destination host in another LISP site, it is highly desirable for it
>    to see the entire path.  Since packets are encapsulated from ITR to
>    ETR, the hop across the tunnel could be viewed as a single hop.
>    However, LISP traceroute will provide the entire path so the user can
>    see 3 distinct segments of the path from a source LISP host to a
>    destination LISP host:
>
>       Segment 1 (in source LISP site based on EIDs):
>
>           source-host ---> first-hop ... next-hop ---> ITR
>
>       Segment 2 (in the core network based on RLOCs):
>
>           ITR ---> next-hop ... next-hop ---> ETR
>
>       Segment 3 (in the destination LISP site based on EIDs):
>
>           ETR ---> next-hop ... last-hop ---> destination-host
>
>    For segment 1 of the path, ICMP Time Exceeded messages are returned
>    in the normal matter as they are today.  The ITR performs a TTL
>    decrement and test for 0 before encapsulating.  So the ITR hop is
>    seen by the traceroute source has an EID address (the address of
>    site-facing interface).
>
>    For segment 2 of the path, ICMP Time Exceeded messages are returned
>    to the ITR because the TTL decrement to 0 is done on the outer
>    header, so the destination of the ICMP messages are to the ITR RLOC
>    address, the source source RLOC address of the encapsulated
>    traceroute packet.  The ITR looks inside of the ICMP payload to
>    inspect the traceroute source so it can return the ICMP message to
>    the address of the traceroute client as well as retaining the core
>    router IP address in the ICMP message.  This is so the traceroute
>    client can display the core router address (the RLOC address) in the
>    traceroute output.  The ETR returns its RLOC address and responds to
>    the TTL decrement to 0 like the previous core routers did.
>
>    For segment 3, the next-hop router downstream from the ETR will be
>    decrementing the TTL for the packet that was encapsulated, sent into
>    the core, decapsulated by the ETR, and forwarded because it isn't the
>    final destination.  If the TTL is decremented to 0, any router on the
>    path to the destination of the traceroute, including the next-hop
>    router or destination, will send an ICMP Time Exceeded message to the
>    source EID of the traceroute client.  The ICMP message will be
>    encapsulated by the local ITR and sent back to the ETR in the
>    originated traceroute source site, where the packet will be delivered
>    to the host.
>
> 9.1.  IPv6 Traceroute
>
>    IPv6 traceroute follows the procedure described above since the
>    entire traceroute data packet is included in ICMP Time Exceeded
>    message payload.  Therefore, only the ITR needs to pay special
>    attention for forwarding ICMP messages back to the traceroute source.
>
> 9.2.  IPv4 Traceroute
>
>    For IPv4 traceroute, we cannot follow the above procedure since IPv4
>    ICMP Time Exceeded messages only include the invoking IP header and 8
>    bytes that follow the IP header.  Therefore, when a core router sends
>    an IPv4 Time Exceeded message to an ITR, all the ITR has in the ICMP
>    payload is the encapsulated header it prepended followed by a UDP
>    header.  The original invoking IP header, and therefore the identity
>    of the traceroute source is lost.
>
>    The solution we propose to solve this problem is to cache traceroute
>    IPv4 headers in the ITR and to match them up with corresponding IPv4
>    Time Exceeded messages received from core routers and the ETR.  The
>    ITR will use a circular buffer for caching the IPv4 and UDP headers
>    of traceroute packets.  It will select a 16-bit number as a key to
>    find them later when the IPv4 Time Exceeded messages are received.
>    When an ITR encapsulates an IPv4 traceroute packet, it will use the
>    16-bit number as the UDP source port in the encapsulating header.
>    When the ICMP Time Exceeded message is returned to the ITR, the UDP
>    header of the encapsulating header is present in the ICMP payload
>    thereby allowing the ITR to find the cached headers for the
>    traceroute source.  The ITR puts the cached headers in the payload
>    and sends the ICMP Time Exceeded message to the traceroute source
>    retaining the source address of the original ICMP Time Exceeded
>    message (a core router or the ETR of the site of the traceroute
>    destination).
>
> 9.3.  Traceroute using Mixed Locators
>
>    When either an IPv4 traceroute or IPv6 traceroute is originated and
>    the ITR encapsulates it in the other address family header, you
>    cannot get all 3 segments of the traceroute.  Segment 2 of the
>    traceroute can not be conveyed to the traceroute source since it is
>    expecting addresses from intermediate hops in the same address format
>    for the type of traceroute it originated.  Therefore, in this case,
>    segment 2 will make the tunnel look like one hop.  All the ITR has to
>    do to make this work is to not copy the inner TTL to the outer,
>    encapsulating header's TTL when a traceroute packet is encapsulated
>    using an RLOC from a different address family.  This will cause no
>    TTL decrement to 0 to occur in core routers between the ITR and ETR.
>
> 10.  Mobility Considerations
>
>    There are several kinds of mobility of which only some might be of
>    concern to LISP.  Essentially they are as follows.
>
> 10.1.  Site Mobility
>
>    A site wishes to change its attachment points to the Internet, and
>    its LISP Tunnel Routers will have new RLOCs when it changes upstream
>    providers.  Changes in EID-RLOC mappings for sites are expected to be
>    handled by configuration, outside of the LISP protocol.
>
> 10.2.  Slow Endpoint Mobility
>
>    An individual endpoint wishes to move, but is not concerned about
>    maintaining session continuity.  Renumbering is involved.  LISP can
>    help with the issues surrounding renumbering [RFC4192] [LISA96] by
>    decoupling the address space used by a site from the address spaces
>    used by its ISPs.  [RFC4984]
>
> 10.3.  Fast Endpoint Mobility
>
>    Fast endpoint mobility occurs when an endpoint moves relatively
>    rapidly, changing its IP layer network attachment point.  Maintenance
>    of session continuity is a goal.  This is where the Mobile IPv4
>    [RFC3344bis] and Mobile IPv6 [RFC3775] [RFC4866] mechanisms are used,
>    and primarily where interactions with LISP need to be explored.
>
>    The problem is that as an endpoint moves, it may require changes to
>    the mapping between its EID and a set of RLOCs for its new network
>    location.  When this is added to the overhead of mobile IP binding
>    updates, some packets might be delayed or dropped.
>
>    In IPv4 mobility, when an endpoint is away from home, packets to it
>    are encapsulated and forwarded via a home agent which resides in the
>    home area the endpoint's address belongs to.  The home agent will
>    encapsulate and forward packets either directly to the endpoint or to
>    a foreign agent which resides where the endpoint has moved to.
>    Packets from the endpoint may be sent directly to the correspondent
>    node, may be sent via the foreign agent, or may be reverse-tunneled
>    back to the home agent for delivery to the mobile node.  As the
>    mobile node's EID or available RLOC changes, LISP EID-to-RLOC
>    mappings are required for communication between the mobile node and
>    the home agent, whether via foreign agent or not.  As a mobile
>    endpoint changes networks, up to three LISP mapping changes may be
>    required:
>
>    o  The mobile node moves from an old location to a new visited
>       network location and notifies its home agent that it has done so.
>       The Mobile IPv4 control packets the mobile node sends pass through
>       one of the new visited network's ITRs, which needs a EID-RLOC
>       mapping for the home agent.
>
>    o  The home agent might not have the EID-RLOC mappings for the mobile
>       node's "care-of" address or its foreign agent in the new visited
>       network, in which case it will need to acquire them.
>
>    o  When packets are sent directly to the correspondent node, it may
>       be that no traffic has been sent from the new visited network to
>       the correspondent node's network, and the new visited network's
>       ITR will need to obtain an EID-RLOC mapping for the correspondent
>       node's site.
>
>    In addition, if the IPv4 endpoint is sending packets from the new
>    visited network using its original EID, then LISP will need to
>    perform a route-returnability check on the new EID-RLOC mapping for
>    that EID.
>
>    In IPv6 mobility, packets can flow directly between the mobile node
>    and the correspondent node in either direction.  The mobile node uses
>    its "care-of" address (EID).  In this case, the route-returnability
>    check would not be needed but one more LISP mapping lookup may be
>    required instead:
>
>    o  As above, three mapping changes may be needed for the mobile node
>       to communicate with its home agent and to send packets to the
>       correspondent node.
>
>    o  In addition, another mapping will be needed in the correspondent
>       node's ITR, in order for the correspondent node to send packets to
>       the mobile node's "care-of" address (EID) at the new network
>       location.
>
>    When both endpoints are mobile the number of potential mapping
>    lookups increases accordingly.
>
>    As a mobile node moves there are not only mobility state changes in
>    the mobile node, correspondent node, and home agent, but also state
>    changes in the ITRs and ETRs for at least some EID-prefixes.
>
>    The goal is to support rapid adaptation, with little delay or packet
>    loss for the entire system.  Heuristics can be added to LISP to
>    reduce the number of mapping changes required and to reduce the delay
>    per mapping change.  Also IP mobility can be modified to require
>    fewer mapping changes.  In order to increase overall system
>    performance, there may be a need to reduce the optimization of one
>    area in order to place fewer demands on another.
>
>    In LISP, one possibility is to "glean" information.  When a packet
>    arrives, the ETR could examine the EID-RLOC mapping and use that
>    mapping for all outgoing traffic to that EID.  It can do this after
>    performing a route-returnability check, to ensure that the new
>    network location does have a internal route to that endpoint.
>    However, this does not cover the case where an ITR (the node assigned
>    the RLOC) at the mobile-node location has been compromised.
>
>    Mobile IP packet exchange is designed for an environment in which all
>    routing information is disseminated before packets can be forwarded.
>    In order to allow the Internet to grow to support expected future
>    use, we are moving to an environment where some information may have
>    to be obtained after packets are in flight.  Modifications to IP
>    mobility should be considered in order to optimize the behavior of
>    the overall system.  Anything which decreases the number of new EID-
>    RLOC mappings needed when a node moves, or maintains the validity of
>    an EID-RLOC mapping for a longer time, is useful.
>
> 10.4.  Fast Network Mobility
>
>    In addition to endpoints, a network can be mobile, possibly changing
>    xTRs.  A "network" can be as small as a single router and as large as
>    a whole site.  This is different from site mobility in that it is
>    fast and possibly short-lived, but different from endpoint mobility
>    in that a whole prefix is changing RLOCs.  However, the mechanisms
>    are the same and there is no new overhead in LISP.  A map request for
>    any endpoint will return a binding for the entire mobile prefix.
>
>    If mobile networks become a more common occurrence, it may be useful
>    to revisit the design of the mapping service and allow for dynamic
>    updates of the database.
>
>    The issue of interactions between mobility and LISP needs to be
>    explored further.  Specific improvements to the entire system will
>    depend on the details of mapping mechanisms.  Mapping mechanisms
>    should be evaluated on how well they support session continuity for
>    mobile nodes.
>
> *10.5.  LISP Mobile Node Mobility
>
>    An mobile device can use the LISP infrastructure to achieve mobility
>    by implementing the LISP encapsulation and decapsulation functions
>    and acting as a simple ITR/ETR.  By doing this, such a "LISP mobile
>    node" can use topologically-independent EID IP addresses that are not
>    advertised into and do not impose a cost on the global routing
>    system.  These EIDs are maintained at the edges of the mapping system
>    (in LISP Map-Servers and Map-Resolvers) and are provided on demand to
>    only the correspondents of the LISP mobile node.
>
>    Refer to the LISP Mobility Architecture specification [LISP-MN] for
>    more details.*
>
> 11.  Multicast Considerations
>
>    A multicast group address, as defined in the original Internet
>    architecture is an identifier of a grouping of topologically
>    independent receiver host locations.  The address encoding itself
>    does not determine the location of the receiver(s).  The multicast
>    routing protocol, and the network-based state the protocol creates,
>    determines where the receivers are located.
>
>    In the context of LISP, a multicast group address is both an EID and
>    a Routing Locator.  Therefore, no specific semantic or action needs
>    to be taken for a destination address, as it would appear in an IP
>    header.  Therefore, a group address that appears in an inner IP
>    header built by a source host will be used as the destination EID.
>    The outer IP header (the destination Routing Locator address),
>    prepended by a LISP router, will use the same group address as the
>    destination Routing Locator.
>
>    Having said that, only the source EID and source Routing Locator
>    needs to be dealt with.  Therefore, an ITR merely needs to put its
>    own IP address in the source Routing Locator field when prepending
>    the outer IP header.  This source Routing Locator address, like any
>    other Routing Locator address MUST be globally routable.
>
>    Therefore, an EID-to-RLOC mapping does not need to be performed by an
>    ITR when a received data packet is a multicast data packet or when
>    processing a source-specific Join (either by IGMPv3 or PIM).  But the
>    source Routing Locator is decided by the multicast routing protocol
>    in a receiver site.  That is, an EID to Routing Locator translation
>    is done at control-time.
>
>    Another approach is to have the ITR not encapsulate a multicast
>    packet and allow the the host built packet to flow into the core even
>    if the source address is allocated out of the EID namespace.  If the
>    RPF-Vector TLV [RPFV] is used by PIM in the core, then core routers
>    can RPF to the ITR (the Locator address which is injected into core
>    routing) rather than the host source address (the EID address which
>    is not injected into core routing).
>
>    To avoid any EID-based multicast state in the network core, the first
>    approach is chosen for LISP-Multicast.  Details for LISP-Multicast
>    and Interworking with non-LISP sites is described in specification
>    [MLISP].
>
> 12.  Security Considerations
>
>    It is believed that most of the security mechanisms will be part of
>    the mapping database service when using control plane procedures for
>    obtaining EID-to-RLOC mappings.  For data plane triggered mappings,
>    as described in this specification, protection is provided against
>    ETR spoofing by using Return- Routability mechanisms evidenced by the
>    use of a 4-byte Nonce field in the LISP encapsulation header.  The
>    nonce, coupled with the ITR accepting only solicited Map-Replies goes
>    a long way toward providing decent authentication.
>
>    LISP does not rely on a PKI infrastructure or a more heavy weight
>    authentication system.  These systems challenge the scalability of
>    LISP which was a primary design goal.
>
>    DoS attack prevention will depend on implementations rate-limiting
>    Map-Requests and Map-Replies to the control plane as well as rate-
>    limiting the number of data-triggered Map-Replies.
>
>    To deal with map-cache exhaustion attempts in an ITR/PTR, the
>    implementation should consider putting a maximum cap on the number of
>    entries stored with a reserve list for special or frequently accessed
>    sites.  This should be a configuration policy control set by the
>    network administrator who manages ITRs and PTRs.
>
> 13.  Prototype Plans and Status
>
>    The operator community has requested that the IETF take a practical
>    approach to solving the scaling problems associated with global
>    routing state growth.  This document offers a simple solution which
>    is intended for use in a pilot program to gain experience in working
>    on this problem.
>
>    The authors hope that publishing this specification will allow the
>    rapid implementation of multiple vendor prototypes and deployment on
>    a small scale.  Doing this will help the community:
>
>    o  Decide whether a new EID-to-RLOC mapping database infrastructure
>       is needed or if a simple, UDP-based, data-triggered approach is
>       flexible and robust enough.
>
>    o  Experiment with provider-independent assignment of EIDs while at
>       the same time decreasing the size of DFZ routing tables through
>       the use of topologically-aligned, provider-based RLOCs.
>
>    o  Determine whether multiple levels of tunneling can be used by ISPs
>       to achieve their Traffic Engineering goals while simultaneously
>       removing the more specific routes currently injected into the
>       global routing system for this purpose.
>
>    o  Experiment with mobility to determine if both acceptable
>       convergence and session continuity properties can be scalably
>       implemented to support both individual device roaming and site
>       service provider changes.
>
>    Here is a rough set of milestones:
>
>    1.  This draft will be the draft for interoperable implementations to
>        code against.  Interoperable implementations will be ready
>        beginning of 2009.
>
>    2.  Continue pilot deployment using LISP-ALT as the database mapping
>        mechanism.
>
>    3.  Continue prototyping and studying other database lookup schemes,
>        be it DNS, DHTs, CONS, ALT, NERD, or other mechanisms.
>
>    4.  Implement the LISP Multicast draft [MLISP].
>
>    5.  *Implement the LISP Mobile Node draft [LISP-MN].
>
>    6.*  Research more on how policy affects what gets returned in a Map-
>        Reply from an ETR.
>
>    6.
>
>    *7.*  Continue to experiment with mixed locator-sets to understand how
>        LISP can help the IPv4 to IPv6 transition.
>
>    7.
>
>    *8.*  Add more robustness to locator reachability between LISP sites.
>
>    As of this writing the following accomplishments have been achieved:
>
>    1.   A unit- and system-tested software switching implementation has
>         been completed on cisco NX-OS for this draft for both IPv4 and
>         IPv6 EIDs using a mixed locator-set of IPv4 and IPv6 locators.
>
>    2.   A unit- and system-tested software switching implementation on
>         cisco NX-OS has been completed for draft [ALT].
>
>    3.   A unit- and system-tested software switching implementation on
>         cisco NX-OS has been completed for draft [INTERWORK].  Support
>         for IPv4 translation is provided and PTR support for IPv4 and
>         IPv6 is provided.
>
>    4.   The cisco NX-OS implementation supports an experimental
>         mechanism for slow mobility.
>
>    5.   Dave Meyer, Vince Fuller, Darrel Lewis, Greg Shepherd, and
>         Andrew Partan continue to test all the features described above
>         on a dual-stack infrastructure.
>
>    6.   Darrel Lewis and Dave Meyer have deployed both LISP translation
>         and LISP PTR support in the pilot network.  Point your browser
>         to http://www.lisp4.net to see translation happening in action
>         so your non-LISP site can access a web server in a LISP site.
>
>    7.   Soon http://www.lisp6.net will work where your IPv6 LISP site
>         can talk to a IPv6 web server in a LISP site by using mixed
>         address-family based locators.
>
>    8.   An public domain implementation of LISP is underway.  See
>         [OPENLISP] for details.
>
>    9.   We have deployed Map-Resolvers and Map-Servers on the LISP pilot
>         network to gather experience with [LISP-MS].  The first layer of
>         the architecture are the xTRs which use Map-Servers for EID-
>         prefix registration and Map-Resolvers for EID-to-RLOC mapping
>         resolution.  The second layer are the Map-Resolvers and Map-
>         Servers which connect to the ALT BGP peering infrastructure.
>         And the third layer are ALT-routers which aggregate EID-prefixes
>         and forward Map-Requests.
>
>    10.  A cisco IOS implementation is underway which currently supports
>         IPv4 encapsulation and decapsulation features.
>
>    11.  A LISP router based LIG implementation is supported, deployed,
>         and used daily to debug and test the LISP pilot network.  See
>         [LIG] for details.
>
>    12.  A Linux implementation of LIG has been made available and
>         supported by Dave Meyer.  It can be run on any Linux system
>         which resides in either a LISP site or non-LISP site.  See [LIG]
>         for details.  *Public domain code can be downloaded from
>         http://github.com/davidmeyer/lig/tree/master.
>
>    13.  An experimental implementation has been written for three
>         locator reachability algorithms.  One is called echo-noncing,
>         which is documented in this specification.  The other two are
>         called TCP-counts and RLOC-probing, which will be documented in
>         future drafts.*
>
>    If interested in writing a LISP implementation, testing any of the
>    LISP implementations, or want to be part of the LISP pilot program,
>    please contact [e-mail].
>
> 14.  References
>
> 14.1.  Normative References
>
>    [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
>               August 1980.
>
>    [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
>               November 1990.
>
>    [RFC1498]  Saltzer, J., "On the Naming and Binding of Network
>               Destinations", RFC 1498, August 1993.
>
>    [RFC1955]  Hinden, R., "New Scheme for Internet Routing and
>               Addressing (ENCAPS) for IPNG", RFC 1955, June 1996.
>
>    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
>               Requirement Levels", BCP 14, RFC 2119, March 1997.
>
>    [RFC2402]  Kent, S. and R. Atkinson, "IP Authentication Header",
>               RFC 2402, November 1998.
>
>    [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
>               IANA Considerations Section in RFCs", BCP 26, RFC 2434,
>               October 1998.
>
>    [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
>               Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
>               March 2000.
>
>    [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
>               via IPv4 Clouds", RFC 3056, February 2001.
>
>    [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
>               of Explicit Congestion Notification (ECN) to IP",
>               RFC 3168, September 2001.
>
>    [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
>               in IPv6", RFC 3775, June 2004.
>
>    [RFC4423]  Moskowitz, R. and P. Nikander, "Host Identity Protocol
>               (HIP) Architecture", RFC 4423, May 2006.
>
>    [RFC4866]  Arkko, J., Vogt, C., and W. Haddad, "Enhanced Route
>               Optimization for Mobile IPv6", RFC 4866, May 2007.
>
>    [RFC4984]  Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
>               Workshop on Routing and Addressing", RFC 4984,
>               September 2007.
>
> 14.2.  Informative References
>
>    [AFI]      IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
>               NUMBERS http://www.iana.org/numbers.html, Febuary 2007.
>
>    [ALT]      Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
>               Alternative Topology (LISP-ALT)",
>               draft-ietf-lisp-alt-01.txt (work in progress), May 2009.
>
>    [APT]      Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
>               L. Zhang, "APT: A Practical Transit Mapping Service",
>               draft-jen-apt-01.txt (work in progress), November 2007.
>
>    [CHIAPPA]  Chiappa, J., "Endpoints and Endpoint names: A Proposed
>               Enhancement to the Internet Architecture", Internet-
>               Draft http://www.chiappa.net/~jnc/tech/endpoints.txt,
>               1999.
>
>    [CONS]     Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A
>               Content distribution Overlay Network  Service for LISP",
>               draft-meyer-lisp-cons-03.txt (work in progress),
>               November 2007.
>
>    [DHTs]     Ratnasamy, S., Shenker, S., and I. Stoica, "Routing
>               Algorithms for DHTs: Some Open Questions", PDF
>               file http://www.cs.rice.edu/Conferences/IPTPS02/174.pdf.
>
>    *[EMACS]    Brim, S., Farinacci, D., Meyer, D., and J. Curran, "EID
>               Mappings Multicast Across Cooperating Systems for LISP",
>               draft-curran-lisp-emacs-00.txt (work in progress),
>               November 2007.*
>
>    [GSE]      "GSE - An Alternate Addressing Architecture for  IPv6",
>               draft-ietf-ipngwg-gseaddr-00.txt (work in progress), 1997.
>
>    [INTERWORK]
>               Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
>               "Interworking LISP with IPv4 and IPv6",
>               draft-ietf-lisp-interworking-00.txt (work in progress),
>               January 2009.
>
>    [LIG]      Farinacci, D. and D. Meyer, "LISP Internet Groper (LIG)",
>               draft-farinacci-lisp-lig-01.txt (work in progress),
>               May 2009.
>
>    [LISA96]   Lear, E., Katinsky, J., Coffin, J., and D. Tharp,
>               "Renumbering: Threat or Menace?", Usenix , September 1996.
>
>    [LISP-MAIN]
>               Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
>               "Locator/ID Separation Protocol (LISP)",
>               draft-farinacci-lisp-12.txt (work in progress),
>               March 2009.
>
>    *[LISP-MN]  Farinacci, D., Fuller, V., Lewis, D., and D. Meyer, "LISP
>               Mobility Architecture", draft-meyer-lisp-mn-00.txt (work
>               in progress), July 2009.*
>
>    [LISP-MS]  Farinacci, D. and V. Fuller, "LISP Map Server",
>               draft-ietf-lisp-ms-01.txt (work in progress), May 2009.
>
>    [LISP1]    Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
>               "Locator/ID Separation Protocol (LISP1) [Routable  ID
>               Version]",
>               Slide-set http://www.dinof.net/~dino/ietf/lisp1.ppt,
>               October 2006.
>
>    [LISP2]    Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
>               "Locator/ID Separation Protocol (LISP2) [DNS-based
>               Version]",
>               Slide-set http://www.dinof.net/~dino/ietf/lisp2.ppt,
>               November 2006.
>
>    [LISPDHT]  Mathy, L., Iannone, L., and O. Bonaventure, "LISP-DHT:
>               Towards a DHT to map identifiers onto locators",
>               draft-mathy-lisp-dht-00.txt (work in progress),
>               February 2008.
>
>    [LOC-ID-ARCH]
>               Meyer, D. and D. Lewis, "Architectural Implications of
>               Locator/ID  Separation",
>               draft-meyer-loc-id-implications-01.txt (work in progress),
>               Januaryr 2009.
>
>    [MLISP]    Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas,
>               "LISP for Multicast Environments",
>               draft-ietf-lisp-multicast-01.txt (work in progress),
>               May 2009.
>
>    [NERD]     Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
>               draft-lear-lisp-nerd-04.txt (work in progress),
>               April 2008.
>
>    [OPENLISP]
>               Iannone, L. and O. Bonaventure, "OpenLISP Implementation
>               Report", draft-iannone-openlisp-implementation-01.txt
>               (work in progress), July 2008.
>
>    [RADIR]    Narten, T., "Routing and Addressing Problem Statement",
>               draft-narten-radir-problem-statement-00.txt (work in
>               progress), July 2007.
>
>    [RFC3344bis]
>               Perkins, C., "IP Mobility Support for IPv4, revised",
>               draft-ietf-mip4-rfc3344bis-05 (work in progress),
>               July 2007.
>
>    [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
>               Renumbering an IPv6 Network without a Flag Day", RFC 4192,
>               September 2005.
>
>    [RPFV]     Wijnands, IJ., Boers, A., and E. Rosen, "The RPF Vector
>               TLV", draft-ietf-pim-rpf-vector-08.txt (work in progress),
>               January 2009.
>
>    [RPMD]     Handley, M., Huici, F., and A. Greenhalgh, "RPMD: Protocol
>               for Routing Protocol Meta-data  Dissemination",
>               draft-handley-p2ppush-unpublished-2007726.txt (work in
>               progress), July 2007.
>
>    [SHIM6]    Nordmark, E. and M. Bagnulo, "Level 3 multihoming shim
>               protocol", draft-ietf-shim6-proto-06.txt (work in
>               progress), October 2006.
>
> Appendix A.  Acknowledgments
>
>    An initial thank you goes to Dave Oran for planting the seeds for the
>    initial ideas for LISP.  His consultation continues to provide value
>    to the LISP authors.
>
>    A special and appreciative thank you goes to Noel Chiappa for
>    providing architectural impetus over the past decades on separation
>    of location and identity, as well as detailed review of the LISP
>    architecture and documents, coupled with enthusiasm for making LISP a
>    practical and incremental transition for the Internet.
>
>    The authors would like to gratefully acknowledge many people who have
>    contributed discussion and ideas to the making of this proposal.
>    They include Scott Brim, Andrew Partan, John Zwiebel, Jason Schiller,
>    Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay Gill, Geoff Huston,
>    David Conrad, Mark Handley, Ron Bonica, Ted Seely, Mark Townsley,
>    Chris Morrow, Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler,
>    Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi
>    Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Roger
>    Jorgensen, Ran Atkinson, Stig Venaas, Iljitsch van Beijnum, Roland
>    Bless, Dana Blair, Bill Lynch, Marc Woolward, Damien Saucez, Damian
>    Lezama, Attilla De Groot, Parantap Lahiri, and David Black.
>
>    In particular, we would like to thank Dave Meyer for his clever
>    suggestion for the name "LISP". ;-)
>
>    This work originated in the Routing Research Group (RRG) of the IRTF.
>    The individual submission [LISP-MAIN] was converted into this IETF
>    LISP working group draft.
>
> Authors' Addresses
>
>    Dino Farinacci
>    cisco Systems
>    Tasman Drive
>    San Jose, CA  95134
>    USA
>
>    Email: [e-mail]
>
>    Vince Fuller
>    cisco Systems
>    Tasman Drive
>    San Jose, CA  95134
>    USA
>
>    Email: [e-mail]
>
>    Dave Meyer
>    cisco Systems
>    170 Tasman Drive
>    San Jose, CA
>    USA
>
>    Email: [e-mail]
>
>    Darrel Lewis
>    cisco Systems
>    170 Tasman Drive
>    San Jose, CA
>    USA
>
>    Email: [e-mail]
>   
>
>
>
> ------------------------------------------------------------------------
>
>
>
>
>
>
>
> ------------------------------------------------------------------------
>
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