Re: [Mpls-interop] MPLS over MPLS-TP

["Adrian Farrel" <[e-mail]>]

Hi,

We have had considerable debate about this in Geneva.
(I think it is probably time to take this discussion to mpls-tp, so I will 
recreate the thread there).

Some data points for this discussion are:

1. What is the service provided by an MPLS-TP network?
Is it (as described in some documents) the provision of pseudowires over an 
MPLS transport network?
Or is it the provision of services (including pseudowires) over an MPLS 
transport network?

2. It there a need to provide demarcation between server traffic and client 
traffic?
There seem to be several reasons why one might do this:
a. architectural beauty
b. consistency with the answer to point 1
   (depending on the answer!)
c. ease of OAM and general management
  (so you can see the demarcation when you sniff the network)
d. To avoid accidental misforwarding of traffic
  For example, consider an MPLS-TP network operated using
  the management plane. In this network it is possible that an
  LSR along the path of an LSP is misconfigured to pop the
  MPLS-TP LSP top label. If what is found underneath is
  either a label from the client label space, or is treated as a label
  (in the case where the payload is IP) we will not spot an error,
  but may misforward traffic.

3. If there is demarcation as suggested in point 2, what is the best way to 
provide demarcation?
a. Encode as a PW with the end of stack set and a PW header according to the 
appropriate PW encoding type.
b. Simply use the end of stack bit to say that we have reached the bottom of 
the MPLS-TP label stack.
(The alternative clearly being that the label stack runs through from the 
client label stack to the server label stack.)

Opinions are needed!

Cheers,
Adrian

----- Original Message ----- 
From: "Drake, John E" <[e-mail]>
To: "Ben Niven-Jenkins" <[e-mail]>om>; 
<[e-mail]>
Sent: Wednesday, December 10, 2008 10:48 PM
Subject: Re: [Mpls-interop] MPLS over MPLS-TP


>
>
>>-----Original Message-----
>>From: Ben Niven-Jenkins [mailto:[e-mail]]
>>Sent: Wednesday, December 10, 2008 2:41 PM
>>To: [e-mail]
>>Subject: [Mpls-interop] MPLS over MPLS-TP
>>
>>Colleagues,
>>
>>What's the current view of how to support MPLS over MPLS-TP?
>>
>>Do we put a PW in the middle (like draft-bryant) or do we just
>>use the label stack and have MPLS directly over MPLS-TP?
>
> JD:  I always thought this was a terrible idea.  Since MPLS-TP is a
> particular MPLS profile and since we said that the MPLS dataplane
> wouldn't be touched, I think we would either add entries to the stack
> (MPLS), or place an IP packet after the stack (IP).
>
>>
>>Advantage of the first is that it gives layer separation (e.g.
>>If the two layers are operated by different parties),
>>advantage of the second is it's probably a bit simpler.
>>
>>Do the drafts we have say anything about the MPLS over MPLS-TP
>>case? Same for IP over MPLS-TP?
>>
>>Thanks
>>Ben
>>
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