Using IPv6 connectivity, an ssh session suddenly hangs, mostly after receiving a bunch of content like "man <something>", "cat <something", or opening a file with "vim" or viewing logfiles with "tail". In most circumstances, the client window is bigger than 80x25. I've traced it down a little bit. 1) keystrokes at the client would be still transferred to the server and "executed", means a ":q" still closes the vi session. But the keystrokes are not echo'ed back 2) tethereal shows following: 4070 2756.543315 3ffe:ffff::2 -> 3ffe:ffff::1 SSH Encrypted response packet len=52 4071 2756.545218 3ffe:ffff::2 -> 3ffe:ffff::1 SSH Encrypted response packet len=52 4072 2756.829811 3ffe:ffff::1 -> 3ffe:ffff::2 TCP 1029 > ssh [ACK] Seq=48912 Ack=613310 Win=8920 Len=0 4073 2756.830219 3ffe:ffff::2 -> 3ffe:ffff::1 SSH Encrypted response packet len=1115 4074 2756.830310 3ffe:ffff::2 -> 3ffe:ffff::1 SSH Encrypted response packet len=517 4075 2756.873108 3ffe:ffff::1 -> 3ffe:ffff::2 TCP 1029 > ssh [ACK] Seq=48912 Ack=615228 Win=8920 Len=0 4076 2756.885979 3ffe:ffff::1 -> 3ffe:ffff::2 TCP 1029 > ssh [ACK] Seq=48912 Ack=615332 Win=8816 Len=0 4077 2757.257207 3ffe:ffff::1 -> 3ffe:ffff::2 TCP 1029 > ssh [ACK] Seq=48912 Ack=616447 Win=8920 Len=0 4078 2757.929816 3ffe:ffff::2 -> 3ffe:ffff::1 SSH [TCP Retransmission] Encrypted response packet len=517 4079 2759.179240 3ffe:ffff::1 -> 3ffe:ffff::2 SSH Encrypted request packet len=52 4080 2759.218775 3ffe:ffff::2 -> 3ffe:ffff::1 TCP ssh > 1029 [ACK] Seq=616964 Ack=48964 Win=15912 Len=0 4081 2759.275688 3ffe:ffff::2 -> 3ffe:ffff::1 SSH [TCP Retransmission] Encrypted response packet len=517 4082 2759.677364 3ffe:ffff::1 -> 3ffe:ffff::2 SSH Encrypted request packet len=52 4083 2759.677741 3ffe:ffff::2 -> 3ffe:ffff::1 TCP ssh > 1029 [ACK] Seq=616964 Ack=49016 Win=15912 Len=0 4084 2759.884709 3ffe:ffff::1 -> 3ffe:ffff::2 SSH Encrypted request packet len=52 4085 2759.885097 3ffe:ffff::2 -> 3ffe:ffff::1 TCP ssh > 1029 [ACK] Seq=616964 Ack=49068 Win=15912 Len=0 4086 2760.110273 3ffe:ffff::1 -> 3ffe:ffff::2 SSH Encrypted request packet len=52 After the retransmission packet, no longer keystrokes are echo'ed back. It's not an IPv6 MTU issue, because the MTU is already set down to 1280. See also: http://thread.gmane.org/gmane.network.ipv6.general/740 This happen using clients like PuTTY (W2K), openssh (on FC2 and FC3) and servers of version openssh-3.9p1 and openssh-3.6p1 (RHEL3, RHEL4, FC3). Any hints how to track this down? I'm partially able to reproduce this (mostly by "tail -f maillog" and waiting some time... For the moment I can supply the tcpdump capturing from tethereal output shown above. But I would also be able to start an additional ssh server with strace. BTW: I already disabled compression, because this can also lead to session hangs on IPv6, already happen in the priv/pub key exchange phase.
*** Bug 1026 has been marked as a duplicate of this bug. ***
I have never seen a problem like this, and I use OpenSSH over IPv6 every day. Could you please send packet traces in tcpdump -vv format rather than tethereal? I suspect that this is a network problem and tcpdump -vv provides better TCP info (and I can read it better)
Will send raw packet capture file directly for keeping privacy.
After some off-bugzilla discussion, this looks increasingly like a broken network stack or a flakey bit of network equipment, reopen if this turns out not to be true.
Change all RESOLVED bug to CLOSED with the exception of the ones fixed post-4.4.