Subject: PWE3 requirements

From: Stewart Bryant <[email-masked]>
Date: Mon, 31 Mar 2003 17:27:29 +0100

The Requirements document says nothing about the issue
of a PW aliasing an IP packet (the CW PID issue). It
is clear from comments on the list that a PW that
does not take this into account will be subject to
disruption when traversing an ECMP enabled MPLS core, and
I raised concerns about psamp/ipfix.

I think that there needs to be a requirement added to
to the effect that a PW must operate correctly over a PSN
that provides ECMP, and a possibly a requirement that
allows IP flow monitoring. Whether this gets resolved in
PWE3 or in MPLS is OoS, but as PWE3 is the first payload
that he IETF has defined that has this problem, it
generates the requirement.

Something like:

"If the PSN uses an ECMP or IP flow recognition method,
then the PW encapsulation must use a method discriminating
between itself and an IP flow"

My personal view is that we should always provide the
discrimination (because that is future proof), but the
text I suggest above says:

"Discriminate if your network needs it. How you discriminate
is up to you i.e. in the CW or by an MPLS extension"

Stewart

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From: "Thomas D. Nadeau" <[email-masked]>
Date: Mon, 31 Mar 2003 12:37:32 -0500

>between itself and an IP flow"

         I think that it is hard to determine if the PSN
employs an ECMP or flow recognition method other
that knowing a priori that they might exist.  I think it
might be more straight-forward to just state,

         "The PW encapsulation must use a method whereby
any PW can be distinguished from other flows traversing the
PSN."

         That seems to cover all the cases.

>is up to you i.e. in the CW or by an MPLS extension"

         Stewart, this sounds reasonable; however, given how
late we are in the game for this document and how much
discussion has been seen on the list for the PID both pro and
con, there definitely should be consensus before we make
such an addition.

         --Tom

>Stewart
>
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http://www.elsevier-international.com/catalogue/title.cfm?ISBN=155860751X

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From: Stewart Bryant <[email-masked]>
Date: Mon, 31 Mar 2003 18:54:25 +0100

>         That seems to cover all the cases.

I am OK with that text.

> con, there definitely should be consensus before we make

Yes, it's a difficult call. I don't want to disrupt the document
and I too am concerned about how late in the day we realised the
need to do this. On the other hand I am also concerned that folks
could argue that the issue is OOS because it unless it is in the
requirements.

Stewart