On 08/30/17 01:33, Philipp Marek wrote: >> sshd also dies when certain other kinds of traffic is generated, such as >> `man pw' using the most pager[1], and many x11 apps such as emacs. >> However, it is stable when running simple x11 apps such as xeyes, and >> the link its self is stable -- a terminal will stay connected without >> issue for days, as long as not much happens in it. Also a sshfs >> connection dies immediately. >> >> ssh -Y karren >> gkrellm & >> *sshd dies* > > My guess is that you *have* an MTU problem on your link, ie. that the > PMTU detection doesn't work; and 1400 might still be too big. > > For a test, please run > > # ping -M do -c 3 -s <size> <peer> > > with size values from 600 to 1400, and then 1450 and 1472. -M do appears to be a linux ping option -- executing from linux. $ ping -M do -c 3 -s 600 karren.example.us PING karren.example.us (67.77.77.777) 600(628) bytes of data. 608 bytes from 67.77.77.777: icmp_seq=1 ttl=55 time=92.8 ms 608 bytes from 67.77.77.777: icmp_seq=2 ttl=55 time=102 ms 608 bytes from 67.77.77.777: icmp_seq=3 ttl=55 time=89.9 ms --- karren.example.us ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2002ms rtt min/avg/max/mdev = 89.956/94.975/102.072/5.171 ms $ ping -M do -c 3 -s 1400 karren.example.us PING karren.example.us (67.77.77.777) 1400(1428) bytes of data. ping: local error: Message too long, mtu=1400 ping: local error: Message too long, mtu=1400 ping: local error: Message too long, mtu=1400 --- karren.example.us ping statistics --- 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2037ms $ ping -M do -c 3 -s 1300 karren.example.us [abbreviating output] 3 packets transmitted, 3 received, 0% packet loss, time 2003ms rtt min/avg/max/mdev = 99.784/106.764/113.670/5.669 ms $ ping -M do -c 3 -s 1372 karren.example.us 3 packets transmitted, 3 received, 0% packet loss, time 6133ms rtt min/avg/max/mdev = 99.977/101.501/102.877/1.244 ms $ ping -M do -c 3 -s 1392 karren.example.us 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2051ms $ ping -M do -c 3 -s 1373 karren.example.us 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2034ms 1372 appears to be the magic number. *repeatingTestsFromFreeBSD* -D appears to be the equivalent of "-M do" $ ping -D -c 3 -s 1373 badger.example.us ping: packet size too large: 1373 > 56: Operation not permitted $ sudo bash # ping -D -c 3 -s 1373 badger.example.us 3 packets transmitted, 0 packets received, 100.0% packet loss # ping -D -c 3 -s 1372 badger.example.us 3 packets transmitted, 3 packets received, 0.0% packet loss round-trip min/avg/max/stddev = 99.126/100.870/102.472/1.370 ms # ifconfig igb0 mtu 1372 (on both ends of the link for good measure) $ ssh karren.example.com $ man pw *linkDies* packet_write_wait: Connection to 67.77.77.777 port 22: Broken pipe Aug 30 12:31:58 karren sshd[28510]: fatal: Fssh_packet_write_poll: Connection from 174.77.777.77 port 49798: Permission denied Darn. > If some size works but the higher ones don't, set the MTU of one of the > machines to the corresponding value, and then establish an SSH connection. > > > Also, if your traceroute has an "--mtu" option, you could run > > # traceroute --mtu <peer> 1472 > > to see some information; but as your ICMPs seem to get filtered, that > might not actually help. $ traceroute --mtu karren.example.us 1373 traceroute to karren.example.us (67.77.77.777), 30 hops max, 1373 byte packets 1 10.0.0.1 (10.0.0.1) 5.500 ms F=1372 7.258 ms 3.027 ms 2 96.120.96.125 (96.120.96.125) 14.881 ms 14.909 ms 18.676 ms And traceroute confirms that the router is restricting packets to 1380. I also tried setting the MTUs down to 600 just to try it, but it didn't seem to make a difference. :( The link still dies. Thank you so much for your suggestions. I think I'm going to try compiling the portable 7.5p1 sshd from a local mirror, and see if it behaves differently. _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
