Subject: more MTU questions
To: None <>
From: Hal Snyder <>
List: tech-net
Date: 10/05/2001 15:41:03
Just wondering if anyone has techniques for working around MTU
problems on a NetBSD router. Specifically, I'm interested in
at least one of the following for transit traffic into a tunnel:
  a. clamping MSS on initial SYN
  b. clearing the DF flag
Newer versions of IOS can do this sort of thing.

Searching has revealed tcpmssd for FreeBSD
an orphan posting on the ipfilter list
and Itojun's fix for NetBSD client(s)

Background - we are having very good results multihoming two sites to
the Internet using NetBSD and Zebra's bgpd. We use a gif tunnel for
the iBGP session between exit routers over private inter-site links.
This is fine except for occasional instances of MTU black-holing
(rfc2923, etc.) which we would like to resolve. Of course the
idealogically pure solution is to LART the remote admins...