Subject: RE: [Fwd: I-D ACTION:draft-bryant-mcpherson-pwe3-cw-00.txt]

From: "Yaakov Stein" <[email-masked]>
Date: Tue, 13 Jul 2004 09:40:30 +0300

Stewart, 

I am sure we are all glad that both of these drafts were written,
and the issue of avoiding problems with ECMP mechanisms
that peek at the MPLS payload is out in the open.

However, the PWE3 draft seems to leave one issue open.

The use of the control word is optional and negotiated.
If it is not used with a MPLS PSN, what are we to do?

If neither CW or PTI is used, then we have potential problems
with ECMP mechanisms.

But the draft says:

   A PW SHOULD employ either the generic PW Control Word described in 
   Section 3, or the PWE3 Payload Type Identifier (PWE3-PTI) described 
   in Section 4. These fields MUST immediately follow the bottom of the 
   MPLS label stack. 

In other words, we only SHOULD use one of the other,
but MUST put them in the right place.

Later, when discussing the PTI the draft says:

  If technical considerations result in a PW Control Word that could 
  be mistaken for an IP packet, the Control Word SHOULD be preceded by 
  a PWE3 Payload Type Identifier (PWE3-PTI). 

This implies that PTIs are only used BEFORE nonstandard CWs
(e.g. CEP headers), but not for packets with no CW at all.

So, are we saying that we from now on, all PWs over MPLS
MUST use CWs  or risk being mistreated by ECMP mechanisms?

BTW - I have another question relating to the statement in the draft :

  The use of any other first nibble value for a PWE3 packet is
deprecated. 

Does the disapproval of values not equal to 0, 1, 4, or 6
result from some further mechanism of which we are unaware?

Y(J)S