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This is a relatively simple trick, but one that I thought was rather clever.

I needed to SSH into a target server ( that only allowed connections from a specific IP address ( I knew that the system holding that specific IP address was down, yet I still needed to SSH into the target.

To further complicate matters, I did not have physical access to the target network at the time. But, I did have remote access (and root) to another Linux box on the network.


So, all I needed to do was change the IP address of my one good box to the one expected by the target system, but if I changed the IP address on the main interface, then I would disconnect myself.

Enter virtual interfaces and routing.

I created a new virtual interface with ifconfig (assuming is the IP we want to come from):

/sbin/ifconfig eth0:1

This does not, however, mean that my SSH connection will come from this address, so I needed to change the routing table (assuming is what we want to connect to):

/sbin/route add -host eth0:1

Now, I will effectively be coming from my new interface when I connect to the target server.