Comments on: RHEL vs SLES: netstat -a

Question: RHEL vs SLES: netstat -a

nomisxid — Tue, 24 Apr 2007 14:33:09 -0800

Why doesn't "netstat -a" work with forwarded ports on SLES 10x64?

I'm doing some testing work on local port forwarding thru ssh. Everything is going along swimmingly as I develop my tests on my RedHat ES4 box. When I go to run my test against a SLES10 x64 machine, things don't work. I believe I have narrowed down the issue to a problem with "netstat -a" not working as expected on the SLES box.

On the RHEL4 box:

[x@localrh .ssh2]$ ssh -oPort=22 -n -L 3434:dragontail:23 x@dragontail sleep 15 &
[1] 26644
[x@localrh .ssh2]$ Authentication successful.
netstat -a | grep 3434
tcp 0 0 localhost.attachmate.c:3434 *:* LISTEN
tcp 0 0 ip6-localhost:3434 *:* LISTEN
[x@localrh .ssh2]$
[1]+ Done ssh -oPort=22 -n -L 3434:dragontail:23 x@dragontail sleep 15

But on SLES10 x64 box:

x@dragontail:~/.ssh2> ssh -oPort=22 -n -L 3434:localrh:23 x@localrh sleep 15 &
[1] 17294
x@dragontail:~/.ssh2> Authentication successful.
x@dragontail:~/.ssh2> netstat -a | grep 3434
x@dragontail:~/.ssh2>
[1]+ Done ssh -oPort=22 -n -L 3434:localrh:23 x@localrh sleep 15

I've verified that the forwarded ports are available and active on the SLES box, just like on the RHEL box, but I can't figure out why it's not showing up in my netstat. A quick googling for SLES and netstat didn't report any unusual behavior. Am I missing something obvious?

By: Malor

Malor — Tue, 24 Apr 2007 14:54:11 -0800

Have you tested to make sure that the ports are actually forwarding correctly? There are settings in /etc/ssh/ssh_client that can disable port forwarding.

I'd suggest running the first command without the & sign and seeing if you get any output... the & might be consigning some kind of error into the bitbucket.

By: Malor

Malor — Tue, 24 Apr 2007 14:54:56 -0800

Sorry, that's /etc/ssh_config, as opposed to /etc/sshd_config. The D configures the local daemon... the no-d version does the local client.

By: nomisxid

nomisxid — Tue, 24 Apr 2007 14:58:44 -0800

I did verify that forwarding is active and working as expected, even when it doesn't show up in the netstat.

There is no additional output from ssh when the command is run in the foreground.

x@dragontail:~/.ssh2> ssh -oPort=22 -n -L 3434:localrh:23 x@localrh sleep 15 &
[1] 18656
x@dragontail:~/.ssh2> Authentication successful.
telnet localhost 3434
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Red Hat Enterprise Linux ES release 4 (Nahant Update 4)
Kernel 2.6.9-42.0.10.EL on an i686
òlogin: x
Password:
Last login: Sat Apr 14 01:52:00 from sugar.attachmate.com
You have new mail.
[x@localrh ~]$

By: nomisxid

nomisxid — Tue, 24 Apr 2007 15:24:22 -0800

FYI, I get the same good results on Solaris 9 and 10. I get the same lack-of-results on SLES9-i386.

By: donut

donut — Tue, 24 Apr 2007 15:26:09 -0800

just an idea, but did you grep for 3434 in netstat -an ?

By: nomisxid

nomisxid — Tue, 24 Apr 2007 15:38:17 -0800

How interesting, the "-n" flag did indeed help. Oddly enough though,

x@dragontail:~/.ssh2> netstat -an | grep 3434
tcp 0 0 127.0.0.1:3434 0.0.0.0:* LISTEN
tcp 0 0 ::1:3434 :::* LISTEN
x@dragontail:~/.ssh2> netstat -a | wc -l
317
x@dragontail:~/.ssh2> netstat -an | wc -l
318

By: nomisxid

nomisxid — Tue, 24 Apr 2007 15:41:14 -0800

Ah-ha moment. SLES appearently ships with something called "openCM" with a predefined port of 3434 in /etc/services. Much is explained. Thanks all'round for the help.