IPv6 Scoped Addresses and Routing Protocols

Hi All,

I raised some questions with Bill Fenner in Minneapolis regarding IPv6 scoped 
addressing and our current IPv6 routing protocol specifications, and Bill suggested 
that I should send my questions to this list for discussion.  So, here they are.

First, some background...

As many of you probably know, IPv6 includes the concept of scoped unicast
addressing -- a unicast address can have link-local scope, site-local scope
or global scope.  The address scopes are defined in the IPv6 Addressing 
Architecture:

http://www.ietf.org/internet-drafts/draft-ietf-ipngwg-addr-arch-v3-07.txt

Additional information can be found in the IPv6 Scoped Address
Architecture:

http://www.ietf.org/internet-drafts/draft-ietf-ipngwg-scoping-arch-03.txt

I would suggest that all of you read the IPv6 Scoped Address Architecture
document, if you haven't already, as it contains information regarding
the expected configuration and forwarding behaviour of IPv6 routers.
It also defines the concept of an IPv6 site, which is important to understanding
the questions that I am about to raise.

In IPv6, there is a concept of site-local addressing that is quite different
from the concept of "net 10" addresses in IPv4.  Sites are administratively
defined entities that must be "convex" (i.e. the best route between two nodes
in the site must, at all scopes, fall completely within the site).  Sites boundaries
run through routers, so a single router (called a site border router (SBR)) can 
have interfaces in more than one site.  And, IPv6 site-local addresses can be 
used for site-constrained communication, even when a site is globally 
connected and global addresses are available. 

Because all site-local addresses use the same well-known site-local prefix, the
only way to tell that a particular site-local address belongs to a particular 
site is to know which site originated the address.  SBRs will need
to enforce site boundaries, not mixing site-local routing information, and not
forwarding packets outside of a given site.  To do this, it is expected that 
SBRs will need to maintain multiple "conceptual routing tables", including one 
site-local routing table for each attached site, and one global routing table. 

Unfortunately, I can't find any indication that these concepts have been reflected 
in the current IPv6 routing protocols.  None of our IPv6 routing protocol documents
deal with site-local boundaries or SBR behaviour explicitly.

There are currently four standards for how IPv6 routes will be handled in BGP, OSPF, 
IS-IS and RIP. I will refer to these documents as BGP-IPv6, OSPF-IPv6 and IS-IS-IPv6,
and RIP-IPv6 respectively:

Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing:
http://www.ietf.org/rfc/rfc2545.txt

OSPF for IPv6 
http://www.ietf.org/rfc/rfc2740.txt

Routing IPv6 with IS-IS:
http://www.ietf.org/internet-drafts/draft-ietf-isis-ipv6-02.txt

RIPng for IPv6
http://www.ietf.org/rfc/rfc2080.txt

So here are my actual questions:

(1) Are the statements regarding the routing system in the IPv6 Scoped Addressing Architecture 
draft valid?  Will they work in real life?  Please read it, and comment to the IPv6 WG if you think that 
there are any issues with what it says.

(2) BGP-IPv6:

BGP-IPv6 states:  "As this document makes no assumption on the characteristics of a particular 
routing realm where BGP-4 is used, it makes no distinction between global and site-local addresses
and refers to both as "global" or "non-link-local"."

Would it ever be reasonable for BGP to propagate site-local routing information?  Why, under
what circumstances?  Would it be reasonable to assume that an Inter-Domain Routing protocol
shouldn't propagate site-local information at all?

If BGP should be capable of propagating site-local information, will it be possible, using existing 
BGP standards for a BGP SBR router with four interfaces (A, B, C & D), in two sites (A & B in S1, 
and C & D in S2) to maintain two separate sets of information for prefix FEC0::/10, one that applies 
to S1 (interfaces A & B) and one that applies to S2 (interfaces C & D), and to propagate that information 
accordingly?  Is this really just an issue of configuring the router properly, as BGP-IPv6 implies?

(3) OSPF-IPV6:

In this specification, no distinction is made between site-local and global addresses.  Unlike the 
previous specification (BGP-IPv6), this assumption is not stated up-front.  Instead, everywhere in
the draft where either site-local or global addresses are mentioned they are both mentioned (i.e.
"site-local or global IPv6 addresses").

Again this specification makes no provision for separate sets of site local information.  There is
also no mention of a boundary for site-local route propagation, and no mention of multiple conceptual
sets of site-local routing information.  Would it make sense to tie the concept of an IPv6 site to 
one of the existing propagation boundaries in OSPF, such as an OSPF area?  Or to assume that
an OSPF AS will always be completely contained within one site -- which is what the current draft
seems to assume?

(4) IS-IS-IPv6:

IS-IS-IPv6 makes no mention of site-local or scoped addressing at all. Is this appropriate?  How will IS-IS 
SBRs know not to propagate site-local routing information between two attached sites?  I don't yet
know enough about IS-IS to understand how site-local routing information would best be handled
in IS-IS.  Any thoughts?

(5) RIP-IPv6:

The RIP-IPv6 document explicitly states that there is a single IPv6 routing table, and it makes no
mention of sites.  I think it would be fine to constrain RIP to operating within a single IPv6
site, but that should be explicitly stated somewhere.

(6) Will the MIBs for any of these routing tables be capable of representing multiple independent,
possibly overlapping sets of site-local routing information?  I looked them over quickly, and it
wasn't immediately obvious to me how they could do this.

(7) Do you think that there would be some utility to defining the actual routing architecture (as
opposed to just the addressing architecture) for IPv6?  If so, what would be the best way to do
that?

(8) Should we mention link-local addresses anywhere in these specifications?  We certainly would
not want to propagate routing information for link-local addresses.

If there is some work that needs to be done here, I am very happy to provide some IPv6 expertise
to that effort.  

Margaret

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