>    Wolfgang>   route add -mtu 4096 -net x.x.x.0 myinterface

 >   Yes, but that isn't the point of PMTU discovery.
 >
 >  The point is to figure out that there are FDDI networks from A<->B
 >and so that *NON-LOCAL* packets can be bigger.
 >  In any case, the reason I wanted PMTU code (which I understand now
 >that FreeBSD has) is because I want to determine if my implementation
 >of PMTU ICMP's in an IPsec security gateway works correctly.

PMTU is also useful if you have an Ethernet subnet at home, with a
SLIP or PPP connection configured to a low MTU (256 bytes) for
latency reasons.