Route ssh to specific gateway

Question

I would like to know how can I force the use of port 22 to the interface I want, any interface, Wi-Fi or Ethernet.
For example route *:22 to Wi-Fi.
I checked route command but it looks like it's not possible.
Any idea?
BSD or Linux commands are welcome.

Answer 1

Regular routing only works in terms of IP addresses and doesn't concern itself with what data (including TCP or UDP) is transferred.

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At least on Linux, you could use policy routing for this:

1. Add a firewall rule to mark certain packets:

   iptables -t mangle -A PREROUTING -p tcp --dport 22 -j MARK --set-mark 1
   

2. Create a new routing table with your desired gateway:

   ip route add default via 192.168.0.1 dev wlan0 table 42
   

3. Add a policy rule to use the new routing table for marked packets:

   ip rule add fwmark 1 table 42
   

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On Windows, you'll need a different approach, for example, telling the program to use a specific interface. Some programs have a "bind address" option, such as ssh's -b:

ssh -b 192.168.0.42 root@myserver

(I don't know how well it works with multiple interfaces, though. I have a feeling it might not.)

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Finally, you could add a host route (via Wi-Fi) towards a specific server.

This could be extended to enabling SSH tunnelling through that server for all your other connections.