Subject: Re: TTL value of VC Label?

From: Stewart Bryant <[email-masked]>
Date: Fri, 02 May 2003 09:00:15 +0100

I could delete the TTL = 2 completely, but there was
some discussion on the list that caused me to add it
in the first place, so how about either something of
the form:

"Ideally the TTL should be a small value to prevent the
looping of PW packets in misconfigured or malfunctioning
MPLS networks. In choosing a suitable TTL value, the
user should give consideration to any PHP systems and
concatonated PWs."

If it needs to be any more complex than this, I will
just delete the sentence.

Stewart

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From: Eric Rosen <[email-masked]>
Date: Fri, 02 May 2003 09:06:22 -0400

Stewart> I could delete the TTL = 2 completely

That would be my preference. 

Olen> I  would  be happy  with  a  statement that  says  when  used in  a
Olen> point-to-point PW environment, the TTL should be set to 2. 

I would  not be  happy with  this.  If your  environment gets  modified, you
shouldn't have to go reconfigure the TTL at all the endpoints.

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From: David Watkinson <[email-masked]>
Date: Fri, 02 May 2003 09:46:54 -0400

Setting the TTL is application dependant.  The originating PE will know
if the PSN tunnel reaches the destination node for the PW.  If it does,
a TTL of 2 is sufficient.  If it does not, the TTL should probably be
set to the configurable default IP TTL to allow for PW stitching.  In
other cases, for example, DTLS, a TTL of 4 may be needed due to the two
additional hops taken between the L2PE and PE at each end.

I would suggest the following text to ensure that the various
applications using PW's think about this issue::

"Setting the TTL is application dependent."

Dave.