The MPLS WG Archive

[Marc Lewis <mlewis@ind.alcatel.com>]

Several recent messages have concerned the issue of how to discern the
Ingress LSR's IP address.  Though it is true that some routers seem to put
it in the Extended Tunnel ID field of the SESSION object,
draft-ietf-mpls-rsvp-lsp-tunnel-08 does not require it.

Furthermore, RFC2205 is not terribly clear about what the phrase "a sender"
means, which is used repeatedly in describing the workings of RSVP message
objects.  Assuming it means the Ingress LSR (the original sender) leads to
one interpretation, and assuming it means the LSR that sent the message
being examined (simply an RSVP peer, not necessarily the Ingress LSR) leads
to another interpretation.  I suspect, but am not certain, the latter
assumption is the correct one.

It does seem reasonably unambiguous, however, that the Ingress and Egress IP
addresses are reliably to be found as the source and destination addresses,
respectively, of the IP header of PATH messages.  Quoting from 3.1.3 in
RFC2205: "Each message contains a sender descriptor defining one sender, and
carries the original sender's IP address as its IP source address".