Russell Coker via luv-main writes:

I've got a Linux system running remotely that has a strange TCP problem, when it sends (not receives) a large packet the connection hangs. For example if I ssh in and run commands with small amounts of output everything is fine, but if I run "ls -l /" then the connection hangs forever.

I had a problem like that once where an ancient OpenBSD (or Solaris?) router was poorly configured. I was told to turn off window scaling on the Linux boxes behind it: sysctl net/ipv4/tcp_window_scaling=0 Eventually, I fixed it properly, by throwing away the broken router. Not sure if that's just broken PMTUD.

On Thursday, 28 April 2016 10:46:31 AM AEST Russell Coker via luv-main wrote:

but "ping -M want -s 1400 8.8.8.8" works without any problems

I usually use "-M do" for that sort of testing. The "tracepath" program will also show you the MTU along the route (as long as UDP isn't being blocked). ...and from bitter experience I would suggest doing the same test in the reverse direction; at work we were having problems for a while with sites outside using jumbo frames until we learnt that the uni had asymetric routing and the return path had a different MTUon one segment to the incoming path. Oh, and some bright spark had decided that they could save IP's by using RFC1918 addresses on those segments and so the router was sending out PMTUD ICMP's with addresses that would get dropped at the border. :-/ Good luck! Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC