[OpenAFS-devel] rx mtu fix

[Marcus Watts]

I don't think you can fix path mtu discovery in RX without finding a
way to set DF in outgoing packets and receive ICMP packets for
when udp packets can't be delivered.  Probably that would be OS
specific (assuming there's a way).  You certainly don't want to use
connected UDP sockets for this.

Looking at the interface is only useful for the first hop, and figuring
out where the first hop goes depends on routing information which (a)
might change and (b) depends on kernel routing logic which has
historically varied a lot and probably isn't very uniform today.
I think it's likely though that the submask is fairly dependable,
since botching the submask often affects connectivity to
local-ish sites.  Looking at the interface & routing record might
be useful for machines only 1 hop away (ie, share the same subnet.)

				-Marcus Watts
				UM ITCS Umich Systems Group