In message <200006140333.e5E3XmL28888@black-ice.cc.vt.edu>, Valdis.Kletnieks@vt .edu writes:
b) If you're a webserver or something else providing service Out There to random users, just nail the MTU at 1500, which will work for any Ethernet/PPP/SLIP out there. And if you're load balancing to geographically disparate servers, then your users are probably Out There, with an MTU almost guaranteed to be 1500.
I assert that the chances of PMTU-D helping are in direct ratio to the number of end users who have connections with MTU>1500 - it's almost a sure thing that you probably won't have users with an MTU on their last-hop that's bigger than their campus backbone and/or Internet connection's MTU.
Is anybody seeing any documentable wins by using PMTU-D?
There are two places where it's very important. First, some server farms are on FDDI rings, so they have a higher MTU. Second -- and this one is growing in importance -- tunnels, for IPsec, PPTP, etc. -- generally have smaller MTUs. This very reply will travel over a tunnel with an MTU of, I believe, 1480. --Steve Bellovin