In message <199802021906.LAA09162@lestat.nas.nasa.gov>Jason Thorpe writes
>On 2 Feb 1998 09:24:49 -0800 
> Wolfgang Rupprecht <wolfgang@wsrcc.com> wrote:
>
> > BTW, NetBSD could do path-MTU discovery, but it is off by default.
>
>There are two reasons it is turned off by default:
>
>	(1) No Black Hole Detection

There aren't alot of obvious ways to do this, but we'll try.
We can always crank down the MTU as we detect timed out packets;
we can't always depend on maintaining the same path during
the course of a connection, so we can't just be especially careful
when initiating a connection.

>	(2) Currently, the routes added by the PMTU engine don't expire.

This is just a matter of writing some code, which I should do 
Real Soon Now.  I suspect that I can't show my face at the next
IETF without it... :-)

Kevin