Re: port forwading problem

From: Andrew Schulman (andrex_at_deadspam.com)
Date: 09/17/04 

Date: Fri, 17 Sep 2004 11:00:25 -0400

> I have three computers: S, C, F
> S is a server for a database package on port 12345
> C is a client
> F is a forwarding machine which connects to the Internet
>
> All three are running Linux with openssh v 3.9p1
>
> F has port forwarding enabled with the following two lines in sshd_config
> AllowTcpForwarding yes
> GatewayPorts yes
>
> On C I run ssh -N -g -L 12345:S:12345 user@F
>
> When I run on C 'telnet localhost 12345' I get an error message in the
> window where I started the port forwarding that says
> 'administratively prohibited: open failed'
> In the logs of F I get
> 'sshd[8025]: error: connect_to S: unknown host (Name or service not known)'
>
> I can logon to the package by doing 'telnet S 12345' from either C or F
> without a problem, but I want to forward through F so external users can
> access this service.
>
> Any hints, pointers, suggestions, or perhaps even a solution?

- crank up the debug level on the ssh client and/or server, and see if
you can get more details.

- "unknown host" = DNS or firewall problem on F? Can you successfully
'telnet S 12345' from a shell session on F?

- use netstat -an | grep 12345 on C before and after starting ssh, to be
sure the port forwarding succeeded.

Good luck,
A. 

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