Subject: Re: Patch for timiting TCP MSS (i.e. for new PPPoE)
To: David Laight <>
From: None <>
List: current-users
Date: 12/04/2001 13:29:45
In message <003f01c17cda$353eafe0$0100a8c0@snowdrop>"David Laight" writes
>Is it possible - of course it is :-) everything is possible... - to
>dynamically determine the TCP MSS for a given connection?

It is certainly possible to detect and work around path MTU
discovery black holes.  Itojun has a patch to do it for NetBSD.
You're describing here pretty much what it does.

The problem is that we're concerned about the *other* end of
the connection, which needs to implement it as well.  It seems
quite a bit tougher to detect this dynamically, and restart
the TCP connection on our end with a smaller TCP MSS.
Proactively making the MSS smaller (without some knowledge
of a problem) sorta ruins the whole point of path MTU discovery.

If you can come up with a way to do it, though, it might
be a win.  Good luck!