Subject: MPLS Label space

From: "Subramania Pillai" <[email-masked]>
Date: Tue, 24 Aug 1999 10:47:48 +0530

Hi,
    Suppose a LSR supports both per platform and per interface label
space. Just by receiving a labeled packet (from shim header), LSR can't 
distinguish whether the incoming label belongs to per platform space or
per interface space. 

  So the LSR has to be configured properly the range of (min and max)
label space for both platform space and per interface space. 

For example 
      interface index
      0 (per-palatform )        16 - 100
      1                         111 - xxx
      2                         111 - xxx
      3                         111 - xxx

This is my understanding. Is it correct?

Thanks
pillai

---

From: Eric Gray <[email-masked]>
Date: Tue, 24 Aug 1999 09:04:41 -0400

> This is my understanding. Is it correct?

Don't think so.

In the per interface case, the LSR must include the interface
on which a label was received when 'making a decision' as to
how to forward the labeled packet.  In the per platform case,
this is not necessarily true.

However, if an LSR does not maintain both per interface and
per platform label spaces on any of the same interfaces, it
might (as purely an implementation choice, since this would
not be visible to other implementations) treat all interfaces
with a per platform label space as a single 'special' input
interface when making a forwarding 'decision'.  This would 
allow interfaces with per interface label spaces to re-use 
labels also being used by interfaces with per platform label 
spaces.

Even if an LSR does not do this, it does not need to use label
ranges.  It needs only NOT to provide labels it has issued in
a per platform label space in Label Mappings provided in any
per interface label space.  This is relatively easy to do by
using a simple and intuitive implementation approach: simply
treat any label issued in a per platform label space as if it
is 'depleted' in all label spaces.  Less intuitively - if you
don't want to withdraw per interface labels in use because of
a 'space collision' - you must treat labels issued in any per 
interface label spaces as 'depleted' from the per platform
label space as well.

Label ranges might be the simplest way to avoid this, but use
of label ranges is in no way required.