On 26 September 2013 16:13, Trent W. Buck <trentbuck@gmail.com> wrote:
Toby Corkindale <toby@dryft.net> writes:
However for some reason path MTU discovery has completely broken when using the newer modem. The primary Linux box is fine, but all clients (whether wired, wireless *or even virtual*) fail to work unless I manually set their interfaces to an mtu of 1492.
No one has mentioned it yet, so I will:
PMTUD needs ICMP to make it through your firewalls, though I forget which types/code(s). Check the firewalls on all relevant hosts.
Indeed. However the firewall configuration hasn't changed at all. I really just unplugged one modem and plugged in a new one. I didn't even reboot the Linux server or restart the pppd process! (I did a bit later once it became clear everything was borked) I don't understand how using a new bridged adsl modem could affect this. I'm really confused :( Could an ADSL modem really be spotting ICMP packets encapsulated in a PPPOE ethernet frame and throwing them out? Seems unlikely. Or could Exetel have decided to start throwing out ICMP packets at their end suddenly after I reconnected with a new model?? None of these are likely cases, but I'm stumped as to what else could be the cause. T