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Re: Seeking Comcast Contact: need to troubleshoot packet loss and/or asymmetric routing issue between Comcast & Onvoy

  • From: Jim Shankland
  • Date: Thu Aug 02 21:38:07 2007

Adrian Chadd wrote:
On Thu, Aug 02, 2007, Jim Shankland wrote:

Linux has a nifty iptables option (clamp-mss-to-pmtu) to rewrite the
MSS in TCP SYN packets when forwarding a packet onto a link with
a lower MTU than the MSS in the packet.  Works like a charm.  If every
packet forwarding device on the Internet did this, PMTUD would not be
needed.  As is, PMTUD is simply broken, due to widespread firewall
misconfiguration.  As in so many other cases of Internet misbehavior,
you can avoid being part of the problem, but you can't be the solution.

.. non-TCP traffic? 

Hmm; I've never actually heard of anybody doing PMTUD on non-TCP
traffic, though it's possible.  Does anybody actually do it?

Jim Shankland