The MPLS WG Archive

[Raghu Thirumalairajan <Raghu@luminousnetworks.com>]

Title: RE: Question about Labels

I am a bit confused; going through rfc3031 [MPLS-ARCH]:

   "If a particular LSR Rd is attached to a particular LSR Ru over two
   point-to-point interfaces, then Rd may distribute to Ru a binding of
   label L to FEC F1, as well as a binding of label L to FEC F2, F1 !=
   F2, if and only if each binding is valid only for packets which Ru
   sends to Rd over a particular one of the interfaces.  In all other
   cases, Rd MUST NOT distribute to Ru bindings of the same label value
   to two different FECs."

Consider the following figure:
      +----+         +----+
   ---| R1 |---------| R2 |---
      +----+         +----+

R1 is connected to R2 over a single multi-access interface (like 100 Mbps ethernet).
Can R2 distribute L to two FEC requests for F1 & F2 (F1 != F2) from R1? Essentially,
can more than one FEC point to an NHLFE if R1 & R2 are connected over a single
non-point-to-point interface? The statement "In all othercases, Rd MUST NOT distribute
to Ru bindings of the same label value to two different FECs." seems
confusing/contradicting to what's stated below...

Thanks in advance
Rgds
-Raghu

-----Original Message-----
From: David Charlap [mailto:david.charlap@marconi.com]
Sent: Monday, January 22, 2001 8:31 AM
To: mpls@UU.NET
Subject: Re: Question about Labels

> Note that per FEC does not necessarily mean per IP prefix.  Multiple
> prefixes that all leave the MPLS cloud through a common router interface
> and have identical traffic characteristics can be considered a single
> FEC and can use a single LSP.