On Thu, Aug 14, 2014 at 1:19 PM, Tom Horsley <horsley1953 at gmail.com> wrote: >> If you look inside the ICMP packet in wireshark, it will tell you >> who sent it and what MTU they said was acceptable. > > Well, I'm definitely drowning in network confusion here :-). > > Everyone's MTU is the default 1500, I checked all systems in > the path. > > The wireshark display says 1516 in the Length column for the > NFS packet that always shows up before the ICMP errors. If I > expand the "IP V4" line in the packet, it says "Total Length: 1500" > for that READDIRPLUS Reply which says 1516 for the capture > length. It also has the "Don't fragment" flag set. > > It looks like the 16 byte extra is confusing it, but I have no > idea why that is different than the IPv4 length info. I thought NFS defaulted to writing 8192 blocks and let the network stack fragment as needed, so having DF set doesn't make much sense. Also, some firewalling schemes have issues with fragments, especially if they arrive out of order - not sure about the new stuff in C7. -- Les Mikesell lesmikesell at gmail.com