Subject: Re: Re: draft-suping-bfd-mpls-fecmismatch-00 questions

From: zhaisuping <[email-masked]>
Date: Sat, 26 Feb 2005 09:41:49 +0800

Hi, all
The purpose of FEC filter in BFD is to detect the consistence of 
the control plane and data plane. So that in the MPLS network, just
running the BFD session(LSP-Ping is not needed) is enough for the
defect detection. Or else such tools as LSP-Ping is needed because
the BFD session can't detect the inconsistence of the control plane
and data plane. 
In the section 2 of the draft, there is description of the 
problem the draft want to solve.
>> Wouldn't LSP-Ping (or VCCV) be a more appropriate place to do this
>> filter verification?

>
>LSP-Ping does a verification on the FEC itself, so a filter would add
>nothing.
>
>VCCV is not a protocol.  Just a little sideband for sending IP packets
>down a pseudowire so that you can run LSP-Ping, BFD, etc. between the
>two ends.
>
>....George
>
>========================================================================
>George Swallow             Cisco Systems                  (978) 936-1398
>                           1414 Massachusetts Avenue
>                           Boxborough, MA 01719

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From: "Thomas D. Nadeau" <[email-masked]>
Date: Sat, 26 Feb 2005 09:15:25 -0500

> the BFD session can't detect the inconsistence of the control plane

	There are cases where BFD/MPLS will work and return
a positive result, but the LSP is actually broken.
If you run LSP ping, this will certainly detect (and report) the
failure.  This is why a combination of both tools is necessary.
BFD with or without your FEC filter will not solve all of the
problems alone.

	--Tom

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From: George Swallow <[email-masked]>
Date: Sat, 26 Feb 2005 11:25:48 -0500

> problem the draft want to solve.

I assume you mean this:

   "The result is that the LDP label is popped in the core of 
   the network, and the popping LSR may attempt to forward the 
   application label."

I'm not particularly persuaded by this example.  A properly designed
router would *not* forward the application label!

...George

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From: David Ward <[email-masked]>
Date: Sun, 27 Feb 2005 09:48:29 -0600

Unfort., what you write is 180 degrees opposite from the charter of the BFD
WG and the philosophy of how the protocol is to function. BFD is not to check
the consistency of the forwarding and control plane. We do not want to 
take this protocol into the realm of control plane failure detection system
(as there are many better protocols or protocol machinery for that) but,  focus
on forwarding failure detection that can send alarms, event notification, diags,
etc up the stack.

-DWard