Sam Stickland writes:
Iljitsch van Beijnum wrote:
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.
Windows Vista/2007 has black hole detection enabled by default. It's not massively elegant, but it will keep sessions up (falls back to 536 byte MTU).
Note that there's a new IETF specification (RFC 4821) for ("Packetization Layer") Path MTU discovery, which doesn't rely on ICMP messages to work. If what I wrote here http://kb.pert.geant2.net/PERTKB/PathMTU is correct, this has been implemented in recent (>= 2.6.17) Linux kernels. I don't know of any other OSes that have this yet - not that they'd tell me (but they could go and edit the page above, that's why it's a Wiki). -- Simon.