Inter-domain FRR Facility backup - discussion

[Arthi Ayyangar <arthi@juniper.net>]

Hi,

Currently the merging of Backup Paths using the Sender Template-specific 
method relies on a different src address, but same LSP ID in the 
SENDER_TEMPLATE for the backup LSP compared to that of the protected LSP. 
(6.1.1 of rfc 4090). After a failure, during local repair, backup LSP Path 
msgs are "tunneled" over the bypass directly to the MP and the Resv from 
MP is IP routed back to the address set in the RSVP_HOP (6.4.3) of the 
backup LSP.

As per the spec, the src address used for backup LSP has to be some 
address on the PLR. I am not sure what the usual practice is, but from 
what I understand, it would be okay currently, to put any local interface 
address on the PLR in the RSVP_HOP as per the spec.

However, when the bypass LSP traverses different domains, and the PLR and 
MP are internal nodes in different domains, the MP is unlikely to have a 
route back to the interface address set in the RSVP_HOP for the backup 
LSP. So it will be unable to route back the Resv to the PLR. This will 
prevent the backup LSP from coming up.

So the issue is finding a way to route back the Resv from MP to PLR.

We could say that in case of inter-domain LSPs, the address that the PLR 
chooses should be the router-id of the PLR. But this has the following 
issues:-
i) If we wan't specific behavior recommendation for inter-domain LSPs,
   then we need to specify conditions to define an LSP as an inter-domain
   LSP at an LSR.
ii) Using router id could increase the chances of this sender template
   (src addr + lsp id) being confused with that of some other LSP being
   originated from this router and terminating on the MP.
ii) For inter-AS LSPs, it may not be common for nodes inside one AS to
    have routes to router-ids (or loopbacks) of "internal nodes" in
    another AS.

Do you see this as an issue worthy of discussion ?
Any ideas / suggestions / recommendations ?

thanks,
-arthi