54 lines
1.9 KiB
HTML
54 lines
1.9 KiB
HTML
<!--# set var="title" value="SSH Tunnelling 101" -->
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<!--# set var="date" value="2006-01-23" -->
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<!--# include file="include/top.html" -->
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<h2>The Players</h2>
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<p>I’ll be referring to 3 hosts:</p>
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<ul>
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<li>A: The server; this machine is behind a firewall that allows outgoing connections but doesn’t allow incoming.</li>
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<li>B: The bounce host; this machine is unfirewalled.</li>
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<li>C: The client.</li>
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</ul>
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<h2>Configuring B</h2>
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<p>Some sshd configuration needs to be done on B before any of this will work. In the sshd_config file (/etc/ssh/sshd_config on Debian):</p>
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<pre><code>AllowTcpForwarding yes
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GatewayPorts yes
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</code></pre>
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<p>Remember to restart sshd after making changes (/etc/init.d/ssh restart).</p>
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<h2>Building the Tunnel</h2>
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<p>On A, run:</p>
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<pre><code>ssh -g -n -R <port on B>:127.0.0.1:<port on A> <address of B> sleep 999999
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</code></pre>
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<p>This will hang with no output; that’s the expected result.</p>
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<p>You should now be able to connect to the port on B and be talking to A. To get this to restart if the connection dies, run it inside:</p>
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<pre><code>while :; do <command>; done
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</code></pre>
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<p>As with all shell commands, put a “&” on the end to run it in the background.</p>
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<h2>Tunnelling FTP</h2>
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<p>Due to a trick in the FTP protocol, you can use this tunnelling arrangement but have FTP data connections go directly from A to C, without touching B. This only works with so-called “active” FTP (using the PORT command instead of PASV). C must also be unfirewalled for this to work.</p>
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<p>The only thing you’ll need to change is the FTP server configuration. In proftpd.conf, add:</p>
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<pre><code>AllowForeignAddress on
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</code></pre>
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<p>For pure-ftpd, run it with the “-w” commandline flag, or with a file named “AllowUserFXP” and a contents of “on” if you’re using pure-ftpd-wrapper.</p>
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<!--# include file="include/bottom.html" -->
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