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Here's the network setup:

Machine A (my PC) SSH 22 => Machine B (Linode with root access) SSH 21343 => Machine C (MySQL server).

I want to forward port 3306 from C through B to A, so I can use SQL Workbench on A to execute commands on C.

Note that C is only accessible over SSH port 21343 and only from B (we cannot change the firewall on C to open any more ports, but we can change its SSH settings).

Is this possible? I've read about tunnels and ProxyCommand. But I need a simple step-by-step example.

All machines are debian Lenny.

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1  
possible duplicate of SSH tunneling and port forwarding –  voretaq7 Aug 28 '11 at 16:54
1  
See the question I marked as a dupe, also see the man page for ssh, specifically the -L option. –  voretaq7 Aug 28 '11 at 16:54
    
The dupe question seems to only refer to two machines. I don't understand it. –  Moishe Mo Aug 28 '11 at 18:07
    
@Moshie - Please read the man page as it explains how to use an intermediate machine (b) to forward ports exactly the way you wish. See also Quanta's answer below. –  voretaq7 Aug 28 '11 at 18:22

3 Answers 3

On the machine A:

ssh -L 3307:C:3306 user@B

This allocated a socket listen to port 3307 on A. And whenever a connection is made to this port, it is forwarded over ssh tunnel to C:3306.

You can then connect to MySQL server on C with:

mysql -u <user> -p -h 127.0.0.1 -P 3307

(127.0.0.1 to connect via TCP/IP instead of a socket)


No, I cannot connect to MySQL on C from B. Only SSH listening on 21343 is open to B.

If the firewall on C only allow to connect from localhost, something like this:

iptables -A INPUT -p tcp -s 127.0.0.1 --dport 3306 -j ACCEPT
iptables -A INPUT -p tcp --dport 3306 -j DROP

so, AFAIK, there is no way to do this. If you try to connect over ssh tunnel, you will get the below errors:

ERROR 2013 (HY000): Lost connection to MySQL server at 'reading initial communication packet', system error: 0
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Only machine B can talk to machine C, and only over SSH port 21343 –  Moishe Mo Aug 28 '11 at 18:04
    
Can you connect to MySQL server on C from B? –  quanta Aug 29 '11 at 2:15
    
Hi Quanta, thanks for the follow-up. No, I cannot connect to MySQL on C from B. Only SSH listening on 21343 is open to B. –  Moishe Mo Aug 31 '11 at 3:12
    
Please check out my above answer. –  quanta Aug 31 '11 at 7:17

~/.ssh/config on machine A looks like this:

Host C
  ProxyCommand ssh -q B nc %h %p
  LocalForward 3306 localhost:3306
  Port 21343

Host B
  Hostname X.X.X.X  (ip of host B)

Then on A ssh C

and in another terminal on A run mysql -h localhost This will connect you to mysql on C over the ssh port forward.

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You might consider something along the lines of http://sourceforge.net/projects/portfwd/ on machine B, possibly listening on something other than TCP 22 so SSH can remain on its standard port for machine B.

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