Re: ICMP_UNREACH_NEEDFRAG returns iface MTU instead of route?

[Jarle Greipsland <jarle%uninett.no@localhost>]

Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost> writes:
[ ... ]
> I, like Greg, had the early reaction that the router shouldn't be using
> the route MTU when forwarding packets (as opposed to processing packets
> originated by the local host-in-the-router).  The reason is that the only
> use I've seen made of the route MTU field is to implement a cache of PMTUs
> discovered by applications running on the local host, and it is normally
> considered quite inappropriate for a router to enforce the PMTUs learned
> by its local applications on packets originated by other hosts.
[ ... ]
Indeed.  Should a downstream router route packets based on source
addresses or some other form of packet classification, the
packets may be sent along paths with different MTUs.  Thus, the
calculated route MTU for the NetBSD forwarder will not
necessarily apply to the traffic from an upstream host.

                                -jarle
-- 
"Once policy-based routing is solved, some new problem with routing
 will arise."                    -- Marshall T Rose