[c-nsp] Question on BGP Link-Local peering...

[Aaron Daubman]

Greetings,

In trying to follow the guidance in
draft-kato-bgp-ipv6-link-local-00.txt while setting up a network using
BGP link-local peering, I came up with a few questions I could not
answer on my own.

First, some network details:
- eBGP sessions will be established across p2p links via link local address
  + each interface on the p2p link will ONLY be addressed with
link-local addresses
  + each router on the ends of the link will have a single global
unicast address tied to a loopback interface.

Part of the draft
(http://www.join.uni-muenster.de/Dokumente/drafts/draft-kato-bgp-ipv6-link-local-00.txt)
states:

"""
A) BGP-4 speakers should ignore the IPv6 global address specified in the
   next hop field in a MP_REACH_NLRI attribute learned over a link-local
   E-BGP session, provided if it does not match with one of the IPv6
   global prefixes assigned to the link. (It is possible to assign an
   IPv6 global prefix to an IX and have a link-local E-BGP session.)
"""

and

"""
C) BGP-4 implementations should be able to configure, at least per
   session basis, which IPv6 global address is to be filled in the next
   hop field of MP_REACH_NLRI attributes.  In the case of link-local E-
   BGP sessions, arbitrary IPv6 address can be specified while in a
   typical case an IPv6 global address attached to the node (other
   interface or loopback) will be specified.
""""

In the network described above, peering will be configured using the
link-local addresses, and the next-hop will be advertised with both
the link-local address as well as the loopback global-unicast address
(via a route-map).

Here are the questions that arose out of this configuration:

1) What does "BGP-4 speakers should ignore the IPv6 global address
specified in the
   next hop field in a MP_REACH_NLRI attribute learned over a link-local
   E-BGP session" mean from A referenced above.  Would not the global
address still need to be used for route propagation, rather than
"ignored"?

2) Stemming from above, if a loopback global address is used as
mentioned in C above ("in a typical case an IPv6 global address
attached to the node (other interface or loopback) will be
specified"), how will nodes in the attached network receiving the
advertisement know how to reach this not-attached next-hop?  I seem to
be missing some magic that would allow this global address to be
reachable and re-advertisable to iBGP peers as the upstream next-hop
(since link-local will be useful only to the direct peer).
- Is the global address ignores as referenced above and such peers
must be configured to next-hop-self to their iBGP neighbors?
- Does each neighbor then need a static route installed to the global
loopback via the link-local address?
- Is there some other behind-the-scenes magic that I'm missing that
informs peer routers how to reach the global loopback address?

Thanks!
     ~Aaron