[Int-area] FYI: draft-despres-sam-02 enclosed

[Rémi Després <[e-mail]>]

Hi,

For your information, draft-despres-sam-02, which was ready too late to be posted before IETF 74, is enclosed below

It is a major update of the version-01 which was presented at IETF 73:
- In Softwires, ref.:
http://www.ietf.org/proceedings/08nov/slides/softwire-3/softwire-3_files/slide0002.htm" rel="nofollow">http://www.ietf.org/proceedings/08nov/slides/softwire-3/softwire-3_files/slide0002.htm 
- In Behave, ref.:
http://www.ietf.org/proceedings/08nov/slides/behave-15.pdf" rel="nofollow">http://www.ietf.org/proceedings/08nov/slides/behave-15.pdf

In San Francisco, its part that deals with NAT66 avoidance is to be discussed at the 6IA BOF meeting (ex NAT66).
Its part that deals with Port-Range extension, is to be discussed at the SHARA BOF.

Comments most welcome. 

Regards,

RD

Internet Engineering Task Force                               R. Despres
Internet-Draft                                             November 2008
Intended status: Standards Track
Expires: May 5, 2009


                    Stateless Address Mapping (SAM)
      Avoiding NATs and restoring the end-to-end principle in IPv6
                          draft-despres-sam-02

Status of this Memo

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Abstract

   Stateless Address Mapping (SAM) is a generic mechanism to support
   global addressing across network zones where routing is based on a
   different address space.  With it, the end-to-end principle, lost in
   IPv4 with the deployment of NATs, can be restored without losing
   services that NAT44s offer beyond address-space extension (private
   addressing, basic firewall, site multihoming, privacy protection,
   host-rooted subnets).  Global-address packets are encapsulated in
   local-address packets to traverse SAM zones, and global prefixes are
   statelessly mapped into local addresses.  For the IPv6-IPv4
   coexistence period, port-restricted IPv4 addresses are used to extend
   the global IPv4 address space.



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Table of Contents

   1.  Introduction and general problem statement . . . . . . . . . .  3
   2.  NAT44 services availability of which in IPv6 is desirable  . .  4
     2.1.  Private addressing (easy renumbering)  . . . . . . . . . .  4
     2.2.  Basic firewall (by default, no incoming connections) . . .  4
     2.3.  Site multihoming (automatic fallback)  . . . . . . . . . .  4
     2.4.  Privacy protection . . . . . . . . . . . . . . . . . . . .  4
     2.5.  Host-rooted subnets  . . . . . . . . . . . . . . . . . . .  5
   3.  SAM specification  . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Local Zones - Root SAMs - Branch SAMs  . . . . . . . . . .  5
     3.2.  Encapsulation of global packets in local packets . . . . .  7
     3.3.  Global prefixes - global addresses - local addresses . . .  9
     3.4.  Endpoint global address to branch local address mapping  . 11
     3.5.  Privacy protection . . . . . . . . . . . . . . . . . . . . 13
     3.6.  SAM parameters . . . . . . . . . . . . . . . . . . . . . . 15
     3.7.  Port-range-based extended IPv4 addressing  . . . . . . . . 16
   4.  SAM Application examples . . . . . . . . . . . . . . . . . . . 17
     4.1.  Address independence in an IPv6 site . . . . . . . . . . . 17
     4.2.  Multihoming and extended IPv4 addressing in a home site  . 19
   5.  SAM as an alternative to NATs in IPv6  . . . . . . . . . . . . 21
   6.  Security considerations  . . . . . . . . . . . . . . . . . . . 22
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 23
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 23
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25
   Intellectual Property and Copyright Statements . . . . . . . . . . 26






















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1.  Introduction and general problem statement

   In IPv4, Network Address Translations have been extensively deployed
   (NAT44s).  They are key to mitigate the IPv4 address shortage.  But
   they also offer various auxiliary services, described in Section 2:
   private addressing, basic firewall, site multihoming, privacy
   protection, host-rooted subnets.

   In counterpart to these auxiliary services, these NAT44s have
   introduced two drawbacks:

   o  Non compliance with the end-to-end principle of the Internet
      (e2e).

         Negative consequences include incompatibility with the IPsec
         security mechanism, and difficulties for hosts to know their
         own global addresses, which they need for connection
         redirections, for host referrals, and and, in sites having
         several site entrance routers, for multihoming support
         mechanisms like the SCTP of [RFC4960] and [Shim6].

   o  Stateful operation.

         Most NAT44s are in fact stateful NAPTs (ref. < xref
         target="RFC2663" />): to support more local addresses than they
         have external addresses, they maintain per-transport-connection
         states.  Negative consequences include limited scalability, and
         the risk of denial of service attacks that go with it, as well
         as single points of failures.

   Since no global address shortage is in view in IPv6, the following
   questions have to be asked:

   o  Which NAT44 services can, in IPv6, be offered statelessly and
      without breaking the e2e principle?

   o  How?

   This draft proposes to answer these questions more completely, and
   with more technical details, than [RFC4864], the most advance
   document on the subject so far.

   For this, a Stateless Address Mapping generic mechanism is introduced
   (SAM).

   Conclusion, is that, provided SAM is supported in nodes at borders of
   independently administered routing zones, the e2e principle can be
   restored in IPv6, for all identified useful functions of NAT44s.



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   (This conclusion needs however to be confirmed after further work on
   SAM details, after criticisms by other experts, after some possible
   bug corrections, and after validations with running code.)

   Thus, traversal of NATs in ISP infrastructures can be avoided.
   (These NATs do provide useful connectivity to some non-SAM-capable
   nodes, but have the drawback of breaking the e2e principle, with the
   mentioned consequences on security, referrals, multihoming,
   scalability and reliability.


2.  NAT44 services availability of which in IPv6 is desirable

2.1.  Private addressing (easy renumbering)

   With NAT44s, when a prefix assigned by an ISPs to a customer site is
   modified, local IP addresses in the site can remain unchanged.

2.2.  Basic firewall (by default, no incoming connections)

   Most NAT44s, being NAPTs, and therefore maintaining states for all
   TCP and UDP connections, have as a byproduct a protection against
   incoming connections (unless some "holes" are "punched" in this
   protection, under explicit customer control).  This level of security
   protection is largely relied upon.

2.3.  Site multihoming (automatic fallback)

   In a site is multi-homed, and if it has a NAT device supporting all
   its ISP interfaces, its hosts can take advantage of multihoming
   without having to support any multihoming-specific function.  This
   level of multihoming support is better than none.

   (For this, a NAT44 needs only to make sure that, for each transport
   connection, all outgoing packets go through the same ISP.  Thus, if
   an ISP access fails, current TCP and UDP connections that go via this
   ISP are broken, but theycan immediately be replaced by new ones.)

2.4.  Privacy protection

   From outside a site where a NAT44 operates in NAPT mode, it is
   difficult to determine which hosts establish which connections.  This
   level of privacy protection, in particular for some web requests, is
   an added value.







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2.5.  Host-rooted subnets

   Behind a host that is assigned a single IPv4 address, it is possible,
   with a NAT44 in the host, to deploy a private subnet.  As modern
   operating systems include a router function with a NAT44, a computer
   can can serve as a root for a LAN.

   Thus, the distinction between hosts and a routers is no longer a
   distinction between types of devices.  It has become only a
   distinction between functions within nodes.


3.  SAM specification

3.1.  Local Zones - Root SAMs - Branch SAMs

   As presented in Figure 1, the SAM mechanism applies to a SAM "local
   zone" Z. Routing within this zone is independently administered, and
   is based on a "local address space".

   Each SAM zone has one or several "root interfaces" (Ri), that give
   access to the global Internet.  Each one has, in the global Internet,
   one or several "global prefixes" (gZij) exclusively assigned to zone
   Z.

   SAM global prefixes can be global IPv6 and/or global IPv4.  SAM local
   address spaces can be IPv6 or IPv4, global or private.  If both IPv4
   and IPv6 are routed in the zone, one of the two is chosen for SAM.
   (SAM is in this respect therefore an extension of the 6to4 of
   [RFC3056], of the ISATAP of [RFC5214], and of [6rd], where all global
   prefixes are IPv6 and all local address spaces are IPv4).

   As explained in Section 3.7, global IPv4 addresses can be extended
   beyond 32 bits to deal with the IPv4 address shortage during the
   IPv4-IPv6 coexistence period.
















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                                         ROOT-SIDE ENDPOINTS
                                      |         /\            |
                                      |         ||            |
                                |_____:_____|   ||     |______:_____|
                                      |                       |
                                      |      ROOT ZONES       |
                                      |                      gZ22
    Zone Global prefixes gZij       gZ11                     gZ21
    Root interfaces:         _________:_______________________:________
                            |(Z)   (root-SAM)              (root-SAM)  |
    Root local addresses:   |         R1                       R2      |
            Ri              |                                          |
                            |                SAM ZONE Z                |
                            |                                          |
                            |                                          |
    Branch local addresses: |      B1               B2           B3   |
            Bk              |      :                :             :    |
    Branch interfaces:      |______:________________:_____________:____|
                                   |                |             |
    Branch Global prefixes:        |          (branch-SAM)        |
      *gBkij=gZij.zBk*               => + gB211, gB221, gB222
    Branch Global Addresses:            +  gB211@, gB221@, gB222@
      *gBkij@=gBkij.H*                              ||
                               BRANCH ZONES         ||
                                                    \/
                                          BRANCH-SIDE ENDPOINTS

                      ROOT AND BRANCH INTERFACES AND SAMs

                                 Figure 1

   Each root interface that supports a root-SAM function has a local
   address (Rk), and each "branch interface" has a local address (Bk).

   If a "branch SAM" function is supported at a branch interface Bk,
   this interface gets, in addition to its local address, global
   prefixes (gBkij).  Each of these prefixes is made of a global prefix
   of the zone (gZij) followed by an identifier (zBk) of the branch in
   its zone.

   For each each of its global prefixes gBkij, a branch interface has
   also a host global address (gBkij@), derived from the prefix by
   appending a standard host suffix (H) to complete the address length.

   Thus, if a zone D is accessible from the global Internet via a zone
   hierarchy A, B, C, it has at least gA.aB.bC.cD as a global prefix gD,
   and gA.aB.bC.cD.H as a global address gD@.  SAM is thus an
   application of the locator-identifier separation principle.  (It



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   differs however from [LISP], in that no new protocol is needed fro
   SAM, just new options in existing protocols such as DHCP [RFC2131],
   DHCPv6 [RFC3315], or ND [RFC4861], to advertise SAM parameters to
   branch interfaces.)

3.2.  Encapsulation of global packets in local packets


   endpoint Y Global address:                 gY
                                               ^
                                               |
                                              ...
   (3)  e2e packet:                    [ gX->gY [data]]
                                               ^
                                               |
                                              gZ         ROOT ZONE R
                                 ______________:______________________
                                |(Z)       (root SAM)                 |
                                |              R         LOCAL ZONE Z |
                                |              ^                      |
                                |              |                      |
                                |             ...                     |
   (2)  encapsulated packet:    |                                     |
         *B = la(gX)*           |      [  B->R [gX->gY[data]]         |
         *R = parameter*        |              ^                      |
                                |              |                      |
                                |              B                      |
                                |______________:______________________|
                                          (branch SAM)   BRANCH ZONE B
                                           => + gB
                                               ^
                                               |
                                              ...
   (1)  e2e packet:                    [ gX->gY [data]]
                                               ^
                                               |
   endpoint X Global address:          gX=gZ.id(B).xxx


     PACKET ENCAPSULATION AND ADDRESS MAPPING - BRANCH SIDE TO ROOT SIDE

                                 Figure 2

   To traverse a SAM local zone, global-address packets are encapsulated
   into local address packets, as illustrated in Figure 2 and Figure 3).

   Thus, compatibility is ensured, within the local zone, with ingress
   the filtering for multihomed networks of [RFC3704], the basic anti-



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   spoofing mechanism.


                                               |
                                               |           ROOT ZONE
                                              gZ
                                 ______________:______________________
                                |(Z)       (root-SAM)                 |
                                |              R         LOCAL ZONE Z |
                                |                                     |
                                |                                     |
                                |                                     |
   (2)  encapsulated packet:    |     [ B1->B2 [gE1->gE2[data]]       |
        *B1 = la(gX)*           |         -------->--------           |
        *B2 = la(gY)*           |       /                   \         |
                                |      ^                     |        |
                                |      |                     v        |
                                |      B1                    B2       |
                                |______:_____________________:________|
           BRANCH ZONES:          (branch-SAM)          (branch-SAM)
                                    => + gB1              => + gB2
                                       ^                     |
                                       |                     v
   (3)  e2e packet:                   ...              [ E1->E2 [data]]
   (1)  e2e packet:             [ E1->E2 [data]]             ...
                                       ^                     |
                                       |                     v
                               gX=gZ.id(B1).xxx         gY=gZ.id(B2).yyy
                                      _:_                   _:_
                                     | X |                 | Y |
                                     |___|                 |___|

   ADDRESS MAPPING AND PACKET ENCAPSULATION - BRANCH SIDE TO BRANCH SIDE

                                 Figure 3

   For the IP-in-IP encapsulation, the IPv6 next header or the IPv4
   protocol id which indicates the type of IP payload is set to 41 (the
   same value as for 6to4, ISATAP, and 6rd).

   Local addresses are determined as follows (illustrated in figures
   Figure 2 and Figure 3):

   1.  If an endpoint global address gE, indifferently source or
       destination, is that of a branch-side endpoint, this is
       recognized by the fact that it starts with one of the global
       prefixes of the zone.  Then, the local address B is obtained by a
       function B=la(gX), completely determined by SAM parameters of the



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       zone (details in Section 3.4).

   2.  If an endpoint global address gE, indifferently source or
       destination, is that of a root-side endpoint, this is recognized
       by the fact that it doesn't start with any of the global prefixes
       of the zone.  In this case, the other address gX of the packet,
       destination or source respectively, is necessarily that of a
       branch-side endpoint (otherwise the packet would not traverse the
       local zone).  Then, local address Ri is that of the root
       interface that has, in its assigned global prefixes, the global
       prefix present at the beginning of the branch-side address gX.

   In multihomed sites, the second of these rules ensures compatibility
   with the ingress filtering of [RFC3704] in root zones (if it does
   apply, as necessary for anti-spoofing protection).

   In Figure 2 and Figure 3, packets in the reverse direction, not
   shown, would have the same addresses but with sources and
   destinations inverted, and with encapsulations and decapsulations
   made at inverted interfaces.

   Decapsulation functions MUST verify, for anti-spoofing protection,
   that local addresses present in headers of encapsulating packets are
   consistent with global addresses present in headers of encapsulated
   packets.

3.3.  Global prefixes - global addresses - local addresses

   Internal structures of SAM global prefixes, global addresses, and
   local addresses are detailed in Figure 4.

   A branch-interface global prefix necessarily starts with a global
   prefix of the zone Z. Its remaining bits are a "branch identifier" in
   the zone (gBkij = gZij.zB).

















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             |<-------------- Branch global address gB@ ------------->|
             |<-------- Branch global prefix gB -------->             |
             |<-- G --><-----  Branch identifier iB ---->             |
              ________________________________________________________
             |  local  |branch|  Subnet |     branch     |   branch   |
             |  zone   |  id  |  index  |      Index     |    Host    |
             |  Global |Format| (option)|                |  endpoint  |
             |  prefix | code |         |                |   suffix   |
             |         |      |         |                | (10...00)  |
             |    G    |   F  |    S    |        I       |     H      |
             |_________|______|_________|________________|____________|
                    _______/   <-- s ---><----- i ------>
                  /               ^                    ^
                 v                |                    |
        Specifies s and b        /                      \
          (option)              |                        \
        Specify F   <-----.-----|--------------------.    \
                           \    |                     \    |
                            \   v                      \   v
                           <-- s --->                 <----- i ------>|
              ________________________________________________________
             |local-address| Subnet  |  next field   |     branch     |
             |   constant  |  index  |   Delimiter   |      index     |
             |    Prefix   |         |   (00...01)   |                |
             |             |         |               |                |
             |       P     |    S    |      D        |        I       |
             |_____________|_________|_______________|________________|
             |<-- subnet prefix zS -->
             |<-------------- Branch local address B ---------------->|


         SAM GLOBAL PREFIXES - GLOBAL ADDRESSES - LOCAL ADDRESSES

                                 Figure 4

   Principles that influence the internal structure of branch
   identifiers proposed for SAM are the following:

   1.  To permit a flexible hierarchy of local zones, branch identifiers
       should be kept rather short.  They should, at least to some
       extent, be proportionate to the maximum number of branches
       supported in their zone.

   2.  Several subnets must be possible in the zone.  For this, a branch
       identifier contain an optional "subnet index" (S), followed the
       "branch index" (I) which identifies the branch in its subnet.
       (The word "index" is chosen to express that these fields have no
       further internal structure.)



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   3.  For the efficiency of routing tables, intra-zone subnet indexes
       have to be in the upper part of local addresses, just behind the
       "constant prefix" (P) that is common to all local addresses.  (In
       IPv6, this constant prefix can typically be an ULA prefix of
       [RFC4193]; in IPv4 is typically a private-address prefix of
       [RFC1918].)

   4.  For efficiency of the neighbor discovery protocol of [RFC2461],
       branch indexes B have on the contrary to be in the lowest part of
       branch local addresses B.

   5.  Consequently, it must be possible to extract separately, from a
       intra-zone branch identifier iB, the subnet index S and the
       interface index I, and for this to know their lengths (s and i).

   6.  In order to permit to configure several subnet-index lengths,
       and/or several interface index lengths, in SAM zones, an optional
       branch-identifier "format code" (F) is placed at the beginning of
       branch identifiers B (just before the optional subnet index S,
       and the branch index B).  Each format codes specifies a subnet-
       index length s and an interface-index length i.  Format codes T
       may have different lengths, but must be non overlapping prefixes
       to be recognized.

   Since the local address B of a branch interface starts with a
   constant prefix P followed by the interface subnet index S , and is
   terminated by the interface-index of the interface, space is left
   between them.  It is filled with a next-field delimiter (D).  Its
   format, a series of 0s followed by a 1, i.e. 00...01 with a minimal
   length of 1 bit, is chosen so that knowing the constant prefix P and
   the subnet prefix of a branch interface, lengths s and i of the its
   subnet index S and of its interface index I can be determined.  Then,
   the identifier format F to be placed in global prefixes of B can be
   derived from these lengths s and i.

3.4.  Endpoint global address to branch local address mapping

   Detailed steps by which a branch local address B is derived from from
   the global address of a branch-side endpoint are presented in
   Figure 5.











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              ________________________________________________________
             |                  Endpoint Global address               |
             |                             gE                         |
             |________________________________________________________|
                           (A) ANALYSIS    ||
                                           \/
              ___________________________________________ ............
             | Global  |  id  |  Subnet |     branch     | endpoint   :
             | prefix  |Format|  index  |      Index     |  suffix    :
             |    G    |   F  |    S    |        I       |     E      :
             |_________|______|_________|________________|............:
                       |   |       |            |
     1. Match found    |   |       |            |
     in the G list  ___|   |       |            |
                           |       |            |
     2. Match found        |       |            |
     in the F list   ______|       |            |
                                   |            |
     3. length defined by F _______|            |
                                   .            |
     4. length defined by F ____________________|
                                   .            .
                 (B) CONSTRUCTION  .     ||     .
                                   .     \/     .
     5. The current                .            .
     local-address prefix __       .            .
                            |      .            .
     6. From step 3. _______:______.__          .
                            |         |         .
     7. From step 4. _______:_________:_________.__________
                            |         |                    |
     8. Binary 00...01 _____:_________:________            |
                            |         |        |           |
              ______________|_________|________|___________|__________
             |  local-address  | Subnet  |next field |     branch     |
             |     Prefix      |  index  | Delimiter |      Index     |
             |         P       |    S    |    D      |        I       |
             |_________________|_________|___________|________________|
             |<--------------- Branch Local address B --------------->|

        DERIVING A BRANCH LOCAL ADDRESS FROM AN ENDPOINT GLOBAL ADDRESS

                                 Figure 5








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3.5.  Privacy protection

   In a zone where privacy protection is desired, the privacy option can
   be turned on.  Principles of this option are the following:

   o  Fields that identify branch-side IP endpoints in privacy protected
      zones, or transport endpoints if endpoints are at this layer, are
      obfuscated in e2e packets that traverse the the global Internet.

   o  This obfuscation is stateless and reversible.

   o  Branch SAMs of a privacy-protected zone are informed of parameters
      of this obfuscation.  They can thus know which "hidden" addresses
      (or addresses plus ports), appear on the global Internet in place
      of their "clear" addresses (or address plus ports).  These clear
      addresses are those from which local addresses are derived in the
      privacy-protected zone and in zones that are lower in the
      hierarchy.

   o  In these lower zones, all branch SAMs are informed that a root SAM
      in the global-Internet direction has activated a privacy option,
      and are informed of parameters of this option.  They can thus
      derive a clear address (or address plus port) from an obfuscated
      address (or address plus port), and conversely.  They can also
      avoid to activate the privacy so that obfuscation is never done
      more than once.

   Parameters of a privacy option are a privacy global prefix (PPm) and
   a scrambling multiplier (PMm).  The prefix is that which, at the
   beginning of global addresses, is not obfuscated in the global
   Internet.  The multiplier is a 64 bit odd constant.

   Obfuscation consists in a modulo 2^n multiplication by the scrambling
   multiplier, where n is the number of bits to be obfuscated.  De-
   obfuscation is the modulo 2^n multiplication by the inverse of the
   scrambling multiplier (for odd numbers, such an inverse modulo 2^n
   always exists).

   In hosts in which the branch SAM is informed of an active privacy
   option, applications that ask for their address and their port at
   their socket interface, get them in hidden form, that which appears
   in the global Internet.  The e2e principle is thus preserved despite
   the fact that the topology of the privacy-protected zone and that of
   lower zones in the hierarchy are all hidden, and despite the fact
   that successive transport connections from a same host cannot, in the
   global Internet, be related to a single host.

   Ports that are concerned with the privacy option are only the IANA



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   defined dynamic and/or private ports (ports 49152 to 65535, those
   starting with binary 11).  Well known ports and registered ports,
   which have an e2e meaning not to be lost must not be obfuscated.

   Since some applications, e.g. active mode FTP of [RFC0959], work on
   port pairs rather than on individual ports, port bits to be
   obfuscated must exclude the las one.  Port bits that are part of
   obfuscated endpoint identifiers are then bits 2 to 14.



                                            gY
                                             ^
                                             |
                                            ...
    e2e packet:              gZ11.F2.hhhh->gY [TCP hh->80 [data]]
                                             ^
                                             |
                                           gZkij         ROOT ZONE R
                  ___________________________:________________________
                 |(Z)             .--> (root SAM)                     |
    Privacy-option ON            /           Rk                       |
    for prefix PP1 = gZkij.F1 ---'           ^          LOCAL ZONE Z  |
    with multiplier PM1                      |                        |
                 |                           |                        |
                 |                          ...                       |
    encapsulated |   [ B->R [ gZkij.cccc->gY [TCP cc->80 [data]]      |
       packet    |                                                    |
                 |                           ^                        |
                 |                           |                        |
                 |                           B                        |
                 |___________________________:________________________|
                                        (branch SAM)
    Clear-address packet:        gZkij.F1.cccc->gY [TCP cc->80 [data]]
    e2e packet:                  gZkij.F1.hhhh->gY [TCP hh->80 [data]]
       where tmp = modulo 2^m (PM1 x (cccc . (bits 2 to 14 of cc))
                   where m = length of cccc + length of cc - 3
             hhhh = bits 0 to (length of hhhh - 1) of tmp
             hh = cc in which bits 2-15 are replaced by
                  bits(length of PP1 TO m - 1) of tmp .

                           SAM PRIVACY OPTION ILLUSTRATION

                                 Figure 6

   Figure 6 illustrates the effect of the privacy option.  The option is
   supposed to be on, in the root SAM of the zone, for its global prefix
   gZkij and its identifier format F1.  The privacy-option prefix is



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   therefore PP1 = gZ11.F2. the scrambling multiplie ris PM1.

3.6.  SAM parameters

   Table 3 to Table 5 of this section present the complete set of SAM
   parameters described in previous sections.

                      +-----------------------+-----+
                      | constant local Prefix | TTL |
                      +-----------------------+-----+
                      |          ...          | ... |
                      |           Pm          | PTm |
                      |          ...          | ... |
                      +-----------------------+-----+

                        CONSTANT PREFIX PARAMETERS

                                  Table 1

   +--------------------+-----+------------------+---------------------+
   |  identifier Format | TTL |   Subnet-index   |   Interface-index   |
   |        code        |     |      Length      |        Length       |
   +--------------------+-----+------------------+---------------------+
   |         ...        | ... |        ...       |         ...         |
   |         Fn         | FTn |        SLn       |         ILn         |
   |         ...        | ... |        ...       |         ...         |
   +--------------------+-----+------------------+---------------------+

                       IDENTIFIER-FORMAT PARAMETERS

                                  Table 2

   +-----------------+-----+---------------+-----+---------------+-----+
   |    Root local   | TTL | Global Prefix | ... | Global Prefix | ... |
   |     address     |     |       1       |     |       j       |     |
   +-----------------+-----+---------------+-----+---------------+-----+
   |       ...       | ... |      ...      | ... |      ...      | ... |
   |        Ri       | RTi |      gZi1     | ... |      gZij     | ... |
   |       ...       | ... |      ...      | ... |      ...      | ... |
   +-----------------+-----+---------------+-----+---------------+-----+

                              ROOT PARAMETERS

                                  Table 3







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                       +--------------------+------+
                       | Global zone prefix |  TTL |
                       +--------------------+------+
                       |         ...        |  ... |
                       |        gZij        | GTij |
                       |         ...        |  ... |
                       +--------------------+------+

                         GLOBAL-PREFIX PARAMETERS

                                  Table 4

        +-----------------------+-----+---------------------------+
        | Privacy-option Prefix | TTL | Privacy-option Multiplier |
        +-----------------------+-----+---------------------------+
        |          ...          | ... |            ...            |
        |          PPp          | PTp |            PMp            |
        |          ...          | ... |            ...            |
        +-----------------------+-----+---------------------------+

                         PRIVACY-OPTION PARAMETERS

                                  Table 5

3.7.  Port-range-based extended IPv4 addressing

   For a dual stack host not to break the e2e principle when it
   establishes a connection with an remote endpoint that is still only
   reachable in IPv4, it must have a global IPv4 address.  Because of
   the IPv4 address shortage, this address may however be shared with
   other hosts.  For this, SAM accepts "port-extended" IPv4 prefixes,
   longer than 32 bits.  Bits beyond the first 32 define a port range in
   the set of dynamic and/or private ports (those in which the two high
   order bits are binary 11).  For example, a 3-bit prefix extension 010
   imposes that branch-side hosts use only ports starting with binary
   11010.

   Note that, due to the systematic encapsulation of global packets in
   local packets of SAM, routing within SAM zones is not concerned with
   theses "port-extended" IPv4 addresses.  Only root SAMs and branch
   SAMs have to know about of port ranges.

   The branch SAM in a host that is assigned a port-restricted IPv4
   address has to inform its socket interface of the port range
   available to applications, and to inform its internal NAT if it has
   one.  Consequences for applications, and for NATs, of restricted port
   ranges, are out of the scope of this SAM specification.  Other
   documents are available on the subject, e.g.  [Boucadair], which



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   however requires further study.


4.  SAM Application examples

4.1.  Address independence in an IPv6 site

   In the example of Figure 7, we consider a home or SOHO site in which
   an Ethernet and/or WiFi LAN is deployed.  Its global IPv6 prefix gZ
   is 2001:0db8:9999::/48.

   Local addressing is done in an IPv6 private space.  To keep address
   shorts in the figure, the constant prefix of these addresses is
   fc00/8, the shortest prefix reserved for private IPv6 addressing in
   [RFC4193].  (This prefix could however be replaced by a full fdxx:
   xxxx:xxxx::/48 prefix, as recommended in [RFC4193] for ULAs, without
   changing the substance of the example.)

   The site is configured to support 255 branch interfaces on the LAN
   (each branch being indifferently a host and/or a router).  To
   facilitate future changes, a branch-identifier format code F1, set to
   0/4, is used in branch global prefixes.

   SAM parameters of the site are then following (ignoring TTLs):

      Constant local prefix: P1 = fc00/8

      Identifier format code: F1 = 0::/4

      Subnet index length: SL1 = 0 (non applicable)

      Interface index length: IL1 = 8

      Root local address: R1 = fc00::0101

      Zone Global prefix: gZ11 = 2001:0db8:9999::/48

      Privacy option prefix: none in this example

   We now consider a SAM-capable PC which serves as a router for a
   bluetooth link.  On this link, a bluetooth mobile phone is active.
   (Configuring a root-SAM in the PC would permit the mobile phone, if
   acting as a SAM-capable router, to assign global prefixes and
   addresses, to hosts behind it.  But this would have been too much for
   the example).






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                                          |
                                          |
                                  2001:0db8:9999::/48
                         _________________:_________________
                        |(Z)       (root SAM) for 2^8 hosts |
                Site    |            fc00::0101             |
               gateway  |                                   |
                        |                                   |
                        |            fc00::0155             |
                        |_________________:_________________|
                                          |
                 Ethernet and/or WiFi    ...
                      fcOO::/64           |

                                      fc00::0155
                                     (branch SAM)
                             => +  2001:0db8:9999:0550::/60
                                __________:__________
                               |2001:0db8:9999:0558::|
               PC              |                     |
                               |_____________________|
                              /___________._________/
                                          |
                  Bluetooth              ...
               2001:0db8:9999:0550::/64   |
                                          |
                            2001:0db8:9999:0550:< eui64 IID >
                                          |
                                        |_|__
                                       |     |
               Mobile phone            |     |
                                       |     |
                                       |_____|

                                 Figure 7

   The PC local address B is fc00::0155, i.e.  P.D.I where P is
   fc00::/8, where the 8 bits of I are supposed to be 55::/8, and where
   D is binary 00...01 with consequently (128 - 8 -8) = 112 bits.

   The PC global prefix gB is therefore 2001:0db8:9999:0550::/60, i.e.
   G.F.I, where G is 2001:0db8:9999::/48, where F is 0::/4, and where I
   is 55::/8.

   The PC global address is therefore 2001:0db8:9999:0558::, i.e. gB.E
   where E is binary 10...00 with (128 - 48 - 4 - 8) = 68 bits.

   The bluetooth link is supposed to have 0::/4 as subnet ID in the PC.



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   Its /64 subnet prefix is therefore 2001:0db8:9999:0550::/64.

   This simple example illustrates how the SAM logic permits to
   establish a hierarchy of routing zones where each host can become a
   router, and where the e2e principle is preserved.

4.2.  Multihoming and extended IPv4 addressing in a home site

   In the example of Figure 8, we consider a home site S, multihomed
   with two ISPs A and B.

   ISP A assigns to the site IPv6 prefix 2001:1111:1111:1110::/60, and
   IPv4 address 192.0.2.1.

   ISP B can only assign port-restricted IPv4 addresses to its sites
   because it has to support up to 2^16 sites, and has only for this an
   IPv4 /18 prefix (namely 198.16.0.0/18, i.e. v4|c610:0000:/18), and
   since 18 + 16 = 34 which exceeds 32.  Having 2001:0db8::/32 as its
   IPv6 prefix, it assigns /48s to its customer sites, in particular
   2001:0db8:0202::/48 to site S.

   Half of its IPv4 address space, namely v4|c608:c000/19 is allocated
   to a NAT to support sites that are not SAM capable.  The other half,
   i.e. v4|c610:2000/19, is allocated to a root SAM, the local address
   of which is supposed to be 2001:0db8::1.

   SAM parameters of the zone of ISP B are then the following:

      Constant local prefix: P1 = 2001:0db8: = v4|a000::/8

      Identifier format code: F1 = ::/0 (non applicable)

      Subnet index length: SL1 = 0 (non applicable)

      Interface index length: IL1 = 16

      Root local address: R1 = 2001:0db8::1:1

      Zone Global prefix: gZ11 = v4|c608:8000/19 (=198.8.128.0/19).

      Privacy option prefix: none in this example (::/0)










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                                                      198.16.0.0/18
                                2001:0db8::/32       =v4|c610:0000:/18
                                  ____|__________________|____________
                                 |(B)             /            \      |
                                 |               |    v4|c610:2000/19 |
                                 |          v4|c608:c000/19      |    |
                                 |             (NAT)       (root SAM) |
                                 |         0.0.0.0/0     2001:0db8::1 |
     |(A)                     |  |                                    |
     |                        |  |                                    |
     |2001:1111:1111:1110::/60|  |   (2^16 SAM sites)                 |
     |       192.0.2.1        |  |                                    |
     |      =v4|c000:0201/32  |  |      2001:0db8:0202::/48           |
     |________________:_______|  |___________________:________________|
                      |                      (branch SAM)
                      |           => + v4|c610:2040:4000::/35
                      |              = 198.8.128.64/ports 11010...
      ________________:______________________________:________________
     |(S)     /               \               /              \        |
     |       |     v4|c000:0201:0000::/33    |  v4|c610:2040:4000::/36|
     |       |                 ::/0          |                 ::/0   |
     | v4|c600:0201:8000::/33   |     v4|c608:2040:6000::/36    |     |
     |     (NAT)            (root SAM)     (NAT)          (root SAM)  |
     |   0.0.0.0/0          fc00::0011    0.0.0.0/0       fc00::0012  |
     |                                                                |
     | (2^4 SAM hosts)                                                |
     |                        fc00::0018                              |
     |_____________________________:__________________________________|
                                   |
           HOST (H)           (branch SAM)
                    => + 2001:1111:1111:1118:8000::0008/64
                       + 2001:0db8:0220:4800::0008/52
           + v4|c000:0201:4000::/37 = 192.0.2.1 ports 1101000...
           + v4|c610:2040:5000::/40 = 198.16.32.64 ports 1101001000...
                                  :
                                  HOST

       PRIVATE-ADDRESSING- AND DUAL-HOMING- SITE WITH E2E CAPABILITY

                                 Figure 8

   In site S, the branch SAM of its root interface with ISP B derives
   from its IPv6 prefix 2001:0db8:O2O2::/48, and from SAM parameters of
   ISP B, its IPv4 prefix v4|c610:2040:4000::/35, which is a port-
   restricted one.

   Two root SAMs are configured in site S. Its local-address constant
   prefix is fc00::/8 as.  Half of the each available IPv4 addressing



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   space is reserved for a NAT, and the other half for a root SAM.

   Parameters of SAMs of site S are then the following:

      Constant local prefix: P1 = fc00/8

      Identifier format code: F1 = 0::/4

      Subnet index length: SL1 = 0

      Interface index length: IL1 = 8

      Root local addresses: R1 = fc00::0011; R2 = fc00::0012

      Zone Global prefixes: gZ11 = 2001:1111:1111:1110::/60; gZ12 = v4|
      c000:0201/32; gz21 = 2001:0db8:0202::/48; gZ22 = v4|
      c610:2040:4000::/35

      Privacy option prefix: none in this example (::/0)

   Among the 16 hosts of home site S, Host H is supposed to have local
   address fc00::0018.  As shown on the figure, the branch SAM of host H
   then derives from this local address two IPv6 global prefixes, two
   IPv6 global host addresses starting with these prefixes, and two
   port-restricted IPv4 prefixes.  With these prefixes, it can use,
   without breaking the e2e principle, 512 ports for connections via ISP
   A, and 64 ports via ISP B.


5.  SAM as an alternative to NATs in IPv6

   With SAM as specified, all NAT44 services that have been listed in
   Section 2 can be offered in IPv6 without stateful processing and
   without breaking the e2e principle:

   1.  In a private-addressing IPv6 site, hosts can know their global
       addresses to use them in e2e packets that are encapsulated in
       local packets to traverse the site.  Renumbering is then
       automated simply by automating advertisement of SAM parameter
       changes (in DHCP and/or with router advertisements).

   2.  The fact that NAT44s are in general configured with by default
       rejection of all incoming calls can have a simple stateless
       equivalent in IPv6:

       *  By default, reject all incoming packets that have a branch-
          side port in the well known or in the IANA defined registered
          port ranges.



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       *  By default, reject all TCP incoming packets that are attempts
          to open new incoming connections (SYN packets without ACK).

   3.  In a SAM-capable site, SAM-capable hosts can take advantage of
       site multihoming with full compatibility with ingress filtering
       of [RFC3704] in both the site itself and in ISP networks to which
       it is connected.

   4.  The privacy protection described in Section 3.5 maintains the e2e
       principle.  It is expected to be largely sufficient in practice.
       (Sophisticated hackers would probably find ways around it, and
       identify who does what in sites havin the privacy-protection
       option, but NAT44s are not perfect for privacy protection
       either).

   5.  As we have seen, SAM global addresses contain a flexible
       succession of branch identifiers, so that it becomes possible to
       set up a flexible hierarchy of private addressing zones.  In
       particular, host-rooted subnets become possible without breaking
       the e2e principle.

   For information, no intellectual property right has been applied for
   by the author on any of SAM mechanisms.  The intent is to facilitate
   IPv6 deployment with new mechanisms that still enhance its potential.


6.  Security considerations

   Like any function where some parameters have to be configured, SAM
   introduces a risk of human errors.

   Besides that, no security risk introduced by SAM has so far been
   identified.  In particular:

   Provided consistency between local addresses present in encapsulating
   packets and global addresses present in encapsulated packets are
   systematic, no more address spoofing is possible than without SAM.

   Due to the stateless operation of SAM, its scalability is high.
   Prevention against denial of service attacks should therefore remain
   easy even for very intense traffic (e.g. using load balancers in
   front of parallel devices).


7.  IANA Considerations

   If and when this specification is stabilized and approved, option
   codes in DHCP, DHCPv6, and ND will have to be defined to



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   automatically convey SAM parameters to branch SAMs.


8.  Acknowledgements

   As this specification has evolved during many months, precious
   encouragement and remarks were received from Mark Townsley.  He has
   to be warmly thanked for it.  Concerning what SAM can bring to port-
   restricted IPv4 addresses, stimulating discussions with Dan Wing,
   Teemu Savolainen, Gabor Bajko, Pierre Levis, Jean-Luc Grimault, and
   Alain Villefranque, have influenced progress of the work.  Gratitude
   is due to them for this.  Challenging remarks, and a few (deserved)
   criticisms from Alain Durand have also helped to better analyze how
   SAM will coexist with NATs.  He deserves credit for it.


9.  References

9.1.  Normative References

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

9.2.  Informative References

   [6rd]      Despres, R., "IPv6 Rapid Deployment on IPv4
              infrastructures (6rd) - Work in progress
              (draft-despres-6rd-02)", October 2008.

   [Boucadair]
              Boucadair, M., Grimault, J-L., Levis, P., and A.
              Villefranque, "Behaviour of BitTorrent service in an IP
              Shared Address Environment



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              (draft-boucadair-behave-bittorrent-portrange-02 - work in
              progress)", january 2009.

   [LISP]     Farinaci, D., Fuller, V., Oran, D., Meyer, D., and S.
              Brim, "Locator/ID Separation Protocol (LISP) -
              draft-farinacci-lisp-09", December 2008.

   [RFC0959]  Postel, J. and J. Reynolds, "File Transfer Protocol",
              STD 9, RFC 959, October 1985.

   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461,
              December 1998.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, August 1999.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3286]  Ong, L. and J. Yoakum, "An Introduction to the Stream
              Control Transmission Protocol (SCTP)", RFC 3286, May 2002.

   [RFC3582]  Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
              Multihoming Architectures", RFC 3582, August 2003.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

   [RFC4219]  Lear, E., "Things Multihoming in IPv6 (MULTI6) Developers
              Should Think About", RFC 4219, October 2005.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4864]  Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
              E. Klein, "Local Network Protection for IPv6", RFC 4864,
              May 2007.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              March 2008.

   [Shim6]    Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming



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              Shim Protocol for IPv6 - Work in progress
              (draft-ietf-shim6-failure-detection-09)", October 2007.

   [draft-carpenter-renum-needs-work-01]
              Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
              still needs work - Work in progress", December 2008.

   [shim6 fail detec]
              Arkko, J. and I. van Beijnum, "Failure Detection and
              Locator Pair Exploration Protocol for IPv6 Multihoming -
              Work in progress (draft-ietf-shim6-failure-detection-09)",
              July 2007.


Author's Address

   Remi Despres
   3 rue du President Wilson
   Levallois,
   France

   Email: [e-mail]





























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Full Copyright Statement

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