PMTU Discovery support

[Kevin Lahey]

On Mon, 19 Mar 2007 14:54:22 -0700
Kevin Lahey <kml at patheticgeek.net> wrote:

> Of course, the real test is to set up a few hosts and see what
> happens, rather than speculating based on a quick perusal of the
> code. :-)

After my slap-dash read of the current FreeBSD code, I was a little
concerned that I'd missed something.  As penance, I set up a quick
experiment with four hosts connected in a line, A <-> B <-> C <-> D,
set the MTU on the links from B to C to 512, and ran ttcp from A to D.
PMTUD worked correctly.  Then I suspended the ttcp process, went away
for an hour, and resumed it. Watching tcpdump, it appears that 512
octet packets continued to be sent, with no attempt at probing.

That would seem to be a bug.

The boxes were running FreeBSD-6.1, but I can't really vouch for the
particular kernel configuration.  It could well be that the problem is
with the loose nut behind the wheel, rather than with FreeBSD. :-)

Kevin
kml at patheticgeek.net