Persistent SSH tunnel with autossh

Overview

To access websites behind an internal network, I proxy web traffic to specific DNS domains over an ssh connection using the SOCKS protocol. The SwitchyOmega plugin takes care of site specific proxying and autossh securely forwards all SOCKS traffic through the ssh tunnel.

To handle network instability, VPN connectivity, and laptop mobility, autossh automatically restarts the ssh tunnel during network changes or failures.

Details

Prerequisite

ssh key authentication must be setup prior to using autossh. The ssh session can not prompt for a password.

Tunnel Setup

Start the ssh tunnel using autossh:

autossh -f -D 5555 -N -M 0 host.example.com

Testing

Test the connection:

[email protected]:~ $ telnet localhost 5555
Trying ::1...
Connected to localhost.
Escape character is '^]'.
quit
Connection closed by foreign host.

Kill the ssh test on the remote site for testing:

# Look for the process without a pty session associated with it
[email protected]:~$ ps -ef | grep ssh | grep jemurray
jemurray 18053 17885  0 15:49 ?        00:00:00 sshd: [email protected]/10
jemurray 20287 20119  0 15:53 ?        00:00:00 sshd: jemurray

# kill the process
[email protected]:~$ kill 20287

The session dies, but automatically restarts:

[email protected]:~ $ telnet localhost 5555
Trying ::1...
Connected to localhost.
Escape character is '^]'.
quit
Connection closed by foreign host.

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