The MPLS WG Archive

["Abes, Andi" <aabes@quarrytech.com>]

Hi, 

I'm trying to resolve a question that looked simple at first:

Is it correct to say that higher level labels can only be drawn from the 
per-platform label space ?

At first it seemed natural, and then I even found in my archives discussions
before the BGP draft was issued that reinforced my conviction:

since packets labeld with BGP labels can arrive at an LSR over different 
interfaces, and the route my vary depending on IGP activity,
at packet reception time - the LSR can not tell by what interface the
labeled
packet should have arrived at.


This is all fine, and sound fine for BGP assigned labels. But...
When labels are assigned using RSVP the whole label stack 
is assigned at once - such that it depends on the semantics  -
is the label stack valid only as a whole ? 
Can the LSR that received the label binding (with 2+ labels)
use the higher levels stacked on other top labels ?

If the former is the case - then per-interface label space can be used.
if the latter, then only per-platform space can be used.

To make things interesting, in draft-swallow-rsvp-bypass-label-00 it
is explicitly assumed that the higher labels can be used with different
top labels (one for the original tunnel and a different one for the bypass
tunnel).

Ok,
so what say you ?


Andi.