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

From: zhaisuping <[email-masked]>
Date: Fri, 25 Feb 2005 09:33:50 +0800

welcome to comments. please see the inline below.
>Zhai -
>
>I'm having a difficult time trying to figure out what problem this
>solves and how it is proposed to be employed.
>
>Of the current proposed MPLS apps for BFD there's VCCV and LSP-Ping
>initiated BFD sessions.  In both cases the FEC binding is established
>before the BFD session comes up.  You have Source and Destination IP
>addresses as well as the pair of discriminators.  This is sufficient to
>ensure that any BFD packet you might accidentally intercept is unique.
>So what extra value comes from the filter???
>

1.Although  FEC binding is established before the BFD session 
comes up, but as in BFD session, the descriminators can be 
changed anytime, so some inconsistence can happen.

2. If the BFD is used to verify the data plane connectivity in 
mpls network, the LSP-Ping or VCCV must be used to check the 
control plane binding. If the FEC filter is used then the BFD
session can do this work, and it would be more authoritative than 
hoping that you did not have collisions in the session 
discriminator space in conjunction with leakage...

---

From: George Swallow <[email-masked]>
Date: Fri, 25 Feb 2005 09:49:45 -0500

> changed anytime, so some inconsistence can happen.

But only the system that is demultiplexing (receiving) can change the
discriminator so how would an inconsistency happen?  Please give a
senario!

> discriminator space in conjunction with leakage...

Again, the receiving system is receiving based on IP address and
demultiplexing based on it's own assigned discriminator.  So how do
"collisions" occur?

...George

========================================================================
George Swallow             Cisco Systems                  (978) 936-1398
                           1414 Massachusetts Avenue
                           Boxborough, MA 01719

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From: Jeffrey Haas <[email-masked]>
Date: Fri, 25 Feb 2005 09:29:37 -0500

Zhai,

> discriminator space in conjunction with leakage...

BFD is meant for detecting whether or not bi-directional forwarding
is working.  LSP-Ping can use BFD to verify that connectivity is
continuous. 

Wouldn't LSP-Ping (or VCCV) be a more appropriate place to do this
filter verification?

-- 
Jeff Haas 
NextHop Technologies

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From: "Thomas D. Nadeau" <[email-masked]>
Date: Fri, 25 Feb 2005 10:12:01 -0500

> changed anytime, so some inconsistence can happen.

	In practice I don't see how this can happen given
that the sessions are bound by unique IP addresses, session
discriminators (and optional security). Can you be more
specific about this failure scenario?

> discriminator space in conjunction with leakage...

	Again, please be more specific about how you think
the use of the tools as specified today will not work.

	--Tom

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From: George Swallow <[email-masked]>
Date: Fri, 25 Feb 2005 11:53:14 -0500

> Wouldn't LSP-Ping (or VCCV) be a more appropriate place to do this

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