Re: ssh connection pause

Hi all, I've finally figured this one out.

After sniffing some traffic I found that, even with "UseDNS no", the sshd
was still performing DNS queries. For some reason in this newer version it
was performing an ipv6 (AAAA) query first, which the DNS server seems to
be silently discarding rather than replying with an NXDOMAIN.

As a workaround I edited /etc/netsvc.conf from "hosts = local, bind" to
"hosts = local, bind4"

Thanks to everyone who replied and helped with this issue.



David R Green <dgreen49@xxxxxxxxxx>
Sent by: listbounce@xxxxxxxxxxxxxxxxx
24/06/2008 03:36 PM

Georgi Stanojevski <glisha@xxxxxxxxx>
Re: ssh connection pause

Hi Georgi,

I provided the output of that in my original post:

From the client:
dgreen49@linuxhost1 [~]# ssh -vvv aixhost1
OpenSSH_4.3p2-hpn, OpenSSL 0.9.7a Feb 19 2003
debug1: Reading configuration data /opt/soe/local/etc/ssh_config
debug2: ssh_connect: needpriv 0
debug1: Connecting to [] port 22.
debug1: Connection established.
debug1: identity file /home/dgreen49/.ssh/identity type -1
debug1: identity file /home/dgreen49/.ssh/id_rsa type -1
debug1: identity file /home/dgreen49/.ssh/id_dsa type -1

<pauses here>

debug1: Remote protocol version 2.0, remote software version
debug1: match: OpenSSH_4.6p1-hpn12v17 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_4.3p2-hpn
debug2: fd 3 setting O_NONBLOCK

From the server:
root@aixhost1 [~]# /opt/soe/local/openssh/sbin/sshd -ddd
debug1: rexec_argv[0]='/opt/soe/local/openssh/sbin/sshd'
debug1: rexec_argv[1]='-ddd'
debug2: fd 3 setting O_NONBLOCK
debug1: Bind to port 22 on
debug1: Server TCP RWIN socket size: 65536
debug1: HPN Buffer Size: 131072
Server listening on port 22.
debug1: fd 4 clearing O_NONBLOCK
debug1: Server will not fork when running in debugging mode.
debug3: send_rexec_state: entering fd = 7 config len 1421
debug3: ssh_msg_send: type 0
debug3: send_rexec_state: done
debug1: rexec start in 4 out 4 newsock 4 pipe -1 sock 7

<pauses here>

debug1: inetd sockets after dupping: 3, 3
Connection from linuxhost1 port 1119



Georgi Stanojevski <glisha@xxxxxxxxx> wrote on 24/06/2008 03:32:28 PM:

David R Green wrote:

I should mention that these AIX servers were successfully running
4.5. It's only since the upgrade to 4.6 that the connection pause

Run the ssh client in verbose mode (ex. ssh -vv user@host) and see where

does the pause happen.