You may see the following error message when attempting to use Transfer Tool:
The "No route to host" error is pretty generic, but it typically means that the source server cannot be reached over the given ports. This is usually caused by a firewall or a network issue.
You can use the steps found in Connection refused when attempting to connect to a remote host to see if either server is blocking the other, and to whitelist each others IP address in the server firewall.
You may also need to ensure the ports are open in the firewall and if you have a network firewall (particularly with a cloud server provider), you'll need to ensure the ports are open there and that the connection isn't being blocked on the network.
You may also want to review How to Troubleshoot Network Issues
If you've done all of this and are still seeing this issue, you'll want to reach out to your datacenter, ISP, or hosting provider to see why the servers aren't able to reach each other.