Subject: [mpls] Doubt on transport address in LDP

From: priyanka gupta <[email-masked]>
Date: Wed, 11 Jun 2008 09:51:13 +0530 (IST)

hi all,
As per RFC 5036"An LSR MUST advertise the same transport address in all Hellos that
   advertise the same label space.  This requirement ensures that two
   LSRs linked by multiple Hello adjacencies using the same label spaces
   play the same connection establishment role for each adjacency."
 
but I found in some router configuration doc that there is an option to configure separetly the transport address per interface.I am not getting the utility of having different transport address on different interface. 

Please help in understanding the benefit of separate transport addrerss over different LDP enabled interface.
Thanks and Regards,
Priyanka Gupta

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From: Mikael Abrahamsson <[email-masked]>
Date: Wed, 11 Jun 2008 08:18:53 +0200 (CEST)

On Wed, 11 Jun 2008, priyanka gupta wrote:

> but I found in some router configuration doc that there is an option to 
> configure separetly the transport address per interface.I am not getting 
> the utility of having different transport address on different 
> interface. 
>

Operationally, I've used it to get around what I interpret as vendor 
incompatibilities. We had routers where the LDP session wouldn't come up 
which was "solved" by using the interface IP as transport address at one 
or both ends.

I've seen vendors interpret the standards differently, where they would 
use the interface IP or loopback IP as source for the multicast packets 
which then contained the loopback address, this caused problems.

I asked about this 1-2 years ago (I think on this list), but received no 
reply as to what was actually the right thing and where this was 
specified, so I basically dropped the issue and did the workaround, 
because I had no leverage towards the vendor to have them "do the right 
thing", as I couldn't find what this was.

-- 
Mikael Abrahamsson    email: [email-masked]