Subject: Re: Unnumbered links in non-GMPLS scenario

From: [email-masked]
Date: Tue, 12 Feb 2002 10:15:25 +200

Yakov, 

>Ania, 
> 
>> I have two questions regarding usage of unnumbered links in plain 
>> MPLS (non-G MPLS) scenario: 
>> 
>> 1) Draft draft-ietf-mpls-rsvp-unnum-03.txt assumes that LSRs exchange 
>> local identifiers assigned to their unnumbered links. Why is it 
>> necessary in non-GMPLS scenario ? By non-GMPLS scenario I mean the 
>> case when RSVP messages are exchanged on the unnumbered links 
>> (data channel is the same as control channel). 
> 
>It was agreed that one always use the IF_ID HOP object on an 
>unnumbered link (see e-mail to the MPLS mailing list on 11/2/2001). 
>And if you use the IF_ID HOP object, then the choice of the data 
>interface is indicated by the upstream node using addresses and 
>identifiers used by the upstream node. 

Does it mean that the upstream node does not have to know 
IF_ID assigned to the interface by the downstream node ? 
The upstream node seams not to use the IF_ID assigned by 
the dowstream node. 

Ania 

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---

From: David Charlap <[email-masked]>
Date: Tue, 12 Feb 2002 10:11:15 -0500

> The upstream node seams not to use the IF_ID assigned by

If traffic engineering is to be used, then the upstream node definitely
needs to know the downstream interface's IF_ID.

The unnumbered interface ERO subobject (defined in the rsvp-unnum draft)
uses this IF_ID to identify a particular unnumbered link when there are
multiple links between two routers.

Right now, the only mechanism where the upstream node can learn this ID
is via the GMPLS extensions to OSPF and ISIS, which is unfortunate,
because it ends up tying the unnumbered interface draft to GMPLS, even
though no GMPLS features are implemented by the draft.

-- David