On 26 September 2013 14:13, James Harper <james.harper@bendigoit.com.au> wrote:
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.
Is it outbound or inbound MTU path discovery that isn't working? Or both?
Hmm, possibly inbound, now you mention it.. I was testing by attempting to curl web pages or images, and didn't try sending anything outbound at the time.
I've had to set MRU explicitly before to get things working properly, although I don't see why the different modem would make a different, unless it was using baby jumbo frames or something.
Both models are 10/100 ethernet only.
What does 'ip link show dev ppp0' say? Is MTU definitely 1492 in there?
Yes, definitely 1492 mtu listed there.
What happens when a client computer tries to send a larger packet? Does your Linux router send a 'frag required' response?
If I'm reading the tcpdump correctly (see reply to myself with it this morning) then yes, there is a frag-required response. T