[rbridge] Choice of routing protocols

[erik.nordmark at sun.com (Erik Nordmark)]

Below is an excerpt from emails between myself and Bob Hinden that tries
to capture some issues around the choice of routing protocol.
Hopefully this can stimulate further discussion on this topic.

    Erik

-------- Original Message --------
Subject: Re: Late agenda item?:  ipvlx charter
Date: Mon, 31 Jan 2005 10:24:35 -0800
From: Erik Nordmark <[e-mail]>
To: Bob Hinden <[e-mail]>


Bob Hinden wrote:

> I also wonder if we want to consider OSPF for this.  The IETF owns all 
> the IPR and can produce derivative standards, where the situation with 
> ISIS is very different (e.g., OSI owns the basic protocol). It's going 
> to be difficult for an L2 bridge implementor to figure out and 
> understand which collection of IETF and OSI specs to use.  Also, if I 
> remember correctly, ISIS still requires manual configuration of 20 byte 
> OSI NSAP addresses.  This would be a pretty odd thing for a L2 bridge.

AFAIK it is only the 6-byte MAC address that is the 'system ID' in
IS-IS. One would probably need to fill in some dummy value for the AFI
and area, but this can be done without any manual config since each box
is assumed to have a factory assigned unique MAC address.

OSPF is a bit harder in fact, since (even with the IPv6 pieces in
OSPFv3) the OSPF router ID is a 4 byte number, and there isn't any
existing numbering space which could be used to create factory assigned
globally unique 32 bit numbers.

While in principle OSPF is interesting and should be explored, there are
some additional items (in addition to the router ID assignment) which
makes using OSPF harder than IS-IS:
  - the OSPF LSAs are specified to carry fixed length addresses (either
    IPv4 or IPv6), so one would probably need to define a new (set of)
    LSAs for TRILL Not a big deal really, but IS-IS was designed to
    handle variable length NLRI from the start.
  - OSPF is designed to run on top of IP whereas IS-IS runs directly on
    IEEE 802.1. While rbridges (just like bridges) will probably be
    assigned IP addresses for management purposes (SNMP), requiring an IP
    address for the rbridge before it can start OSPF do build the
    topology would be a severe limitation. One would want to allow
    rbridges that don't have IP addresses (e.g. for home), or where the
    IP addresses are assigned after the rbridges have established
    connectivity across the link (assigned using stateless IPv6 or DHCP
    for instance).
    [Bob later told me: A possible choice when using OSPF is to use
    OSPFv3 over IPv6 and IPv6 link-local addresses, since any device with
    an IEEE MAC address can form an IPv6 link-local address.]

So trust me, I did really like to use OSPF here, because of the IS-IS
specification issues but also because there are more open source OSPF
code out there for implementors to reuse.


> While on the general topic, RIPv2 might even be a reasonable choice for 
> routing technology.  It's a lot simpler to implement and would still 
> work a lot better than spanning tree.

TRILL does add one additional constraint on a routing protocol (beyond
carrying MAC addresses around) which is to be able to construct a
spanning tree between the rbridges. The spanning tree is needed for
flooding (ARP, ND, and any other broadcast/multicast). Doing this in a
link state protocol is relatively easy; each router can independently
calculate the spanning tree in a consistent manner. But it is far from
clear whether this can be be done in a distance vector protocol.

Also, part of the goal for TRILL is to be better than the IEEE 802.1D
spanning tree, which has a worst-case convergence time of 45 seconds or
so. It isn't clear that RIP is a good fit for fast convergence.

> My general question is:  Is the decision on the routing technology to be 
> used for this going to be something that the w.g. decides or is it just 
> assumed it is ISIS?  I would favor the former approach, but in either 
> case I think it is important that the charter clarify this.

The TRILL WG would need to make the choice.
If the actual routing protocol work is farmed out to the specific,
long-lived routing protocol WGs, the success would depend on those WGs
having interest in this space.
An option is that the TRILL WG define the
extension to the routing protocols, and just have that reviewed by the
routing protocol WG(s).

    Erik
From erik.nordmark at sun.com  Fri Feb  4 12:03:30 2005
From: erik.nordmark at sun.com (Erik Nordmark)
Date: Fri Feb  4 12:04:52 2005
Subject: [rbridge] Conflicts to avoid for BoF/WG?
Message-ID: <[e-mail]>


Are there other conflicts which we must avoid?

    Erik


This might be approved as a WG before the meeting, but we will schedule
it as a BoF for the time being.

    a. Working Group or BOF full name with acronym in brackets:
	TRansparent Interconnection of Lots of Links (TRILL)
    b. AREA under which Working Group or BOF appears:
	INT
    c. CONFLICTS you wish to avoid, please be as specific as possible:
	multi6, shim6, ipv6, v6ops, is-is, ospf

    d. Expected Attendance (figures from the previous IETF are sent when
       WG/BOF scheduling opens)
	100 (based on IPVLX BoF)

    e. Special requests (i.e. multicast):
    f. Number of slots:
	1

    g. Length of slot:
       	2 1/2 hours

Bof Description: See proposed charter below.
This is a follow-on to the IPVLX BoF in Aug 2004

Bof Chair: Erik Nordmark <[e-mail]>

Mailing list: [e-mail]
Subscribe: http://www.postel.org/mailman/listinfo/rbridge
Web page: http://www.postel.org/rbridge/
	With additional information as well as mailing list archives


Agenda:
-------

  - Welcome and Administrivia			5 minutes	Chair

  - Charter review				10 minutes	Chair

  - Problem statement discussion			30 minutes	Erik Nordmark
	Including the "service" that a cloud of hybrid devices will
	provide, whether it is equivalent to IEEE 802.1D devices, or
	handles IP packets differently
	When is it ok to reorder packets? MTU considerations?


  - Threats and security considerations		10 minutes	???
     	What should the goal be? What can we do better?

  - Requirements on routing protocols		20 minutes	???
     	For zero configuration
     	Carrying MAC addresses
     	Broadcast
     	IS-IS vs. OSPF vs. something else

  - Connecting different L2 types		30 minutes	Radia Perlman?

  - Choices for ARP/ND				10 minutes	???
    	Constraints from security discussion (intentionally duplicate L2
	addresses), mobility, SeND support, etc.


  - Choices for broadcast/multicast		10 minutes	???
	Worth doing any optimizations? Spanning tree between rbridges?



Proposed charter:
-----------------

TRansparent Interconnection of Lots of Links (TRILL)


While IEEE 802 bridges are attractive due to not needing explicit
configuration and allowing hosts to move within the bridged topology,
they are more limited than IP routers since bridges
only support IEEE 802 technologies, and the most common layer 2
interconnection method (dynamically created spanning tree
formation using bridges) is not as flexible and robust as layer 3 routing.

The WG will design a hybrid solution that combines the simplicity of
configuration while taking full advantage of complex topologies.

The design should have the following properties:
  - zero configuration of the hybrid devices
  - ability for hosts to move without changing their IP address
  - it should be possible to forward packets using pair-wise shortest paths,
    and exploit the redundant paths through the network for increased
    aggregate bandwidth
  - possible optimizations for ARP and Neighbor Discovery packets 
(potentially
    avoid flooding all the time)
  - support Secure Neighbor Discovery
  - the packet header should have a hop count for robustness in the presence
    of temporary routing loops
  - nodes should be able to have multiple attachments to the network
  - no delay when a new node is attached to the network
  - multicast should work (and after a re-charter it might make sense to
    look at optimizations for IP multicast)
  - be no less secure than existing bridges (and explore whether the 
protocol
    can make "L2 address theft" harder or easier to detect)

A required piece of the solution is an IP routing protocol which is extended
to carry L2 address reachability, handle broadcast, and is friendly to
zero-configuration. Likely candidate are the link-state routing protocols
since they can easily be extended to provide for broadcast, which is 
believed
to be difficult for distance vector protocols.
This working group will define the requirements on such routing protocol(s),
and select the routing protocol(s) to be used.  The intent is that the 
actual
extensions to the routing protocol(s) be performed in the WGs with 
expertise
in the routing protocol(s).

The working group will look into solutions that can interconnect different
layer 2 technologies, and also look at providing support for non-IP 
protocols,
even though one can not combine those two features together; the
interconnection of different layer 2 technologies (with different layer 2
address formats) will most likely only work for the IP family of protocols.
Whether the same or different address formats are used, there might be a 
need
to handle different MTUs.

The WG will design a protocol that combines the benefits of bridges
and routers in a way that will co-exist with existing hosts, IP routers
and bridges. The design must support both IPv4 and IPv6

The working group will not work any layer 3 aspects except to provide
  - Possible optimizations for ARP and ND packets (not always
    flooded everywhere)
  - Being able to carry IP broadcast and multicast packets (which might 
just
    fall out from supporting L2 multicast)
  - Defining the L3 operations needed to interconnect different L2 
technologies


The work consists of several, separable pieces:
  - Defining the requirement on the routing protocol(s), and select one or
    more routing protocols. The detailed specification of the extensions to
    a particular routing protocol will be left as an action item for the
    specific routing protocol WG.
  - Defining what information must be carried in an encapsulation header for
    data packets, and how to map that information to various link types 
(e.g.,
    IEEE LAN, Fibrechannel, MPLS)
  - Defining how address resolution (ARP and Neighbor Discovery) is 
performed,
    taking into account the desire to be compatible with Secure Neighbor
    Discovery.
  - Defining how the solution extends to the case when multiple layer 2
    technologies, that have different address format/length, are 
interconnected.

Deliverables
  - A short draft on the problem statement and goals
  - A document defining what information needs to be carried in routing
    protocols to support the trill concept, and other requirements on
    the routing protocols.
  - Encapsulation draft specifying what needs to be carried in general
    and the specific format to use on IEEE LANs
  - ARP and ND draft
  - Draft on interconnecting different types of layer 2 technologies
  - Threat analysis document

Goals and Milestones

Jun 05  Problem statement and Goals submitted to IESG for Informational
Sep 05  Routing protocol support requirements to IESG for Informational
Dec 05  Encapsulation document to IESG for Proposed Standard
Sep 05  ARP & ND to IESG for Proposed Standard
Mar 06  Interconnecting Layer 2 Technologies document to IESG for
         Proposed Standard
Dec 05  Threat analysis to IESG for Informational

---