On 20 aug 2008, at 20:04, Valdis.Kletnieks at vt.edu wrote: > Hypothetically true. Unfortunately, enough places do bozo > firewalling and drop > the ICMP Frag Needed packets to severely limit the utility of PMTU > Discovery. Yet all OSes have it enabled and there is no fallback to fragmentation in PMTUD: if your system doesn't get the ICMP messages, your session is dead in the water.