Path MTU discovery ICMP messages

Posted at 2:30 pm in Uncategorized

This is more for my own reference… After configuring my ADSL modem to run i bridge mode, it seems I’m running into a few path MTU issues. To identify any path MTU messages, I’ve been analyzing the traffic on the outside interface looking for path MTU issues using the following tcpdump syntax:

tcpdump -n -s0 -i ppp0 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'

Update: Of course, this exact syntax is documented on tcpdump’s own site

Written by bjorn on February 24th, 2011