Re: sysctl options for Maximum segment size

[Hannah Schroeter <uk1o@rz.uni-karlsruhe.de>]

Hello!

On Fri, Dec 01, 2000 at 07:42:33AM +0100, Rémi Guyomarch wrote:
> [...]

> 2) OpenBSD 2.7 doesn't have PMTU discovery, I believe 512 is just low
> enough to cross most routers without getting into MTU
> problems. OpenBSD 2.8 have PMTU discovery, but maybe the default
> didn't get changed.

OpenBSD 2.8 however does not respect
net.inet.tcp.mssdflt, even if
net.inet.ip.mtudisc = 0

Neither does it respect the manual route MTU setting on the
route used (default), but instead it derives a MSS from the
interface MTU. That leads to problems, as I explicitly set
those values (mssdflt and the MTU on the default route) in
order to work around MTU problems (excess fragmentation or
PMTU problems for other boxes which, for some reason, don't
get the "need to fragment" ICMP packets).

> [...]

Kind regards, Hannah.