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[PWE3] LDP DoD and PW Signalling ...

<N.Leymann@telekom.de> Mon, 27 June 2011 07:41 UTC

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From: N.Leymann@telekom.de
To: mpls@ietf.org, pwe3@ietf.org
Date: Mon, 27 Jun 2011 09:41:13 +0200
Thread-Topic: LDP DoD and PW Signalling ...
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Subject: [PWE3] LDP DoD and PW Signalling ...
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Hi,

We came across an issue related to the Seamless MPLS Architecture when running LDP DoD between two nodes if we are trying to set up an PW between the same nodes.

Assume we have an Access Node (AN) and an Aggregation Mode (AG). The AN establishes a LDP DoD with the AG. When we are going to establish a PW between the AN and the AG as well we run into the problem that RFC4447 specifies only the DU mode for the targeted LDP session (section 3):

   "An LDP session must be set up between the pseudowire endpoints.
    LDP MUST be used in its 'downstream unsolicited' mode.  LDP's
    'liberal label retention' mode SHOULD be used."

>From our point of view we should reuse the existing LDP session and go with only a single LDP session between AN and AG. That has the advantage that we do not change the behaviour of PW FECs 128/129 (there are other options like using two LDP sessions with additonal lookbacks or two sessions with single loopback and LDP DoD for IP FECs, but those have an heavy -  negative impact - on the existing implementations and/or standards).

For a more long term approach we are in favour of a change to RFC5036 by defining a new TLV which denotes the DU/DoD mode per FEC type.

Any comments on that?

  Regards

     Nic

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