4.13.5 ‘Logical name of remote host’

This allows you to tell PuTTY that the host it will really end up connecting to is different from where it thinks it is making a network connection.

You might use this, for instance, if you had set up an SSH port forwarding in one PuTTY session so that connections to some arbitrary port (say, localhost port 10022) were forwarded to a second machine's SSH port (say, foovax port 22), and then started a second PuTTY connecting to the forwarded port.

In normal usage, the second PuTTY will access the host key cache under the host name and port it actually connected to (i.e. localhost port 10022 in this example). Using the logical host name option, however, you can configure the second PuTTY to cache the host key under the name of the host you know that it's really going to end up talking to (here foovax).

This can be useful if you expect to connect to the same actual server through many different channels (perhaps because your port forwarding arrangements keep changing): by consistently setting the logical host name, you can arrange that PuTTY will not keep asking you to reconfirm its host key. Conversely, if you expect to use the same local port number for port forwardings to lots of different servers, you probably didn't want any particular server's host key cached under that local port number. (For this latter case, you could instead explicitly configure host keys in the relevant sessions; see section 4.20.2.)

If you just enter a host name for this option, PuTTY will cache the SSH host key under the default SSH port for that host, irrespective of the port you really connected to (since the typical scenario is like the above example: you connect to a silly real port number and your connection ends up forwarded to the normal port-22 SSH server of some other machine). To override this, you can append a port number to the logical host name, separated by a colon. E.g. entering ‘foovax:2200’ as the logical host name will cause the host key to be cached as if you had connected to port 2200 of foovax.

If you provide a host name using this option, it is also displayed in other locations which contain the remote host name, such as the default window title and the default SSH password prompt. This reflects the fact that this is the host you're really connecting to, which is more important than the mere means you happen to be using to contact that host. (This applies even if you're using a protocol other than SSH.)