Subject: Re: FW: BFD for PW Fault Detection (VCCV)

From: George Swallow <[email-masked]>
Date: Thu, 11 May 2006 15:30:27 -0400

Oren -

> If I understand correctly, when using PWE3 VCCV, the BFD packets should be
> UDP/IP packets.
> 
> What is the use of the UDP/IP encapsulation?

When we started this, the "Channel Type" field was just going to use PPP
code-points.  The Control Channel is supposed to be able to multiplex
traffic.  So the UDP part was certainly necessary.

For certain MPLS Ping/Trace functions the IP addresses are also useful.

When I proposed using BFD I suggested getting a PPP code point that
meant "UDP" so that you could skip the IP header when it wasn't
needed. I didn't get a lot of support for the idea and ran into some
opposition.  

The opposition came from two directions.  

OAM wonks who were worried about the 1 in a zillion chance that a BFD
packet from some other router happens to arrive with a label that
matches a valid PW label and has the right discriminators.  (I don't
know how such people get any sleep at all!)

The other came from the PPP side who just said to use PW header
compression.  

Now that the "Channel Type" field has it's own IANA space, we could
probably get a codepoint for BFD and do just what you want.  The one fly
in the ointment is that PW stitching could make it harder to identify
the true source making that one in a zillion a mere one in a billion or
so.

If you really want something then you should raise it on the PW list.

...George

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