Testing a Reverse SSH Tunnel

Scenario:

You want to test connectivity of a Fivetran reverse SSH tunnel that is being used for a database connector or for your destination. 

Fivetran Recommendation:

There are a couple different tests you can run from the virtual machine (VM) running your SSH server to ensure that the reverse tunnel is working as expected:

1. Test a generic SSH connection between your VM and Fivetran's.
   Run:

   ssh fivetran@<FIVETRAN_SUPPLIED_IP>

   If this doesn't work, check firewalls on both sides and run the following test:
   1. Confirm whitelisting is configured correctly by having each machine attempt to ping each other (icmp protocol must be open on each machine/network).
      Run:

      ping <DATABASE_IP>

2. Confirm that your VM is able to access your database.
   Run:

   telnet <DATABASE_IP> <DATABASE_PORT>

3. Test One-Time Port Routing.
   Run:
   

   ssh <FIVETRAN_SSH_USERNAME>@<FIVETRAN_SUPPLIED_IP> -R 
   <SSH_HIGH_PORT>:<DATABASE_IP>:<DATABASE_PORT>

Considerations:

If you are new to working with reverse SSH tunnels, here is a helpful diagram to visualize how they are implemented in Fivetran:

This is also a good quick read on explaining how reverse SSH tunnels work: https://unix.stackexchange.com/questions/46235/how-does-reverse-ssh-tunneling-work