Subject: Re: wg last call on ldp-based vpls solutions

From: Yakov Rekhter <[email-masked]>
Date: Thu, 15 Apr 2004 09:57:05 -0700

Folks,

>From 10.2.2 (Failure detection and recovery) of the draft:

   The MTU-s device controls the usage of the pseudowires to the PE-rs
   nodes.  Since LDP signaling is used to negotiate the pseudowire
   labels, the hello messages used for the LDP session can be used to
   detect failure of the primary pseudowire.

The document needs to clarify whether the LDP session SHOULD be
used to detect failure of the primary pseudowire, or whether the
LDP session MAY be used to detect failure of the primary pseudowire.
And if the latter, then the document should mention other alternatives.

The document also should note that using LDP session for the purpose
of detecting failure of the primary pseudowire can not detect
failure in the data/forwarding plane of the pseudowire, and that
such failures may result in persistent service disruption.

Yakov.

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From: Ali Sajassi <[email-masked]>
Date: Thu, 15 Apr 2004 14:40:10 -0700

>such failures may result in persistent service disruption.

If PE-rs is the next hub from MTU-s, then data and control path coincide 
and hello messages should be sufficient (which might have been the original 
intend). But if they are not, then (VCCV or LSP) BFD or (VCCV or LSP) ping 
can be used to check the health of PWs. Also, if fast detection is needed, 
it may not be appropriate to try to tweak the LDP session timers. So, we 
may want to just use VCCV/LSP based OAM tools in lieu of LDP hello.

-Ali