How did you change this?
I think that you are talking about that you changed the "Home Directory"
to "A redirection to a URL". If you did this, it is expected that it does
not work. A redirection is a redirection, which means that the client
sends a new request to the new server. In your case, it means that the
external client tries to access a server named "webserver", which seems to
be an internal name that cannot be exposed to the public. Since this name
is only available on the LAN, the external client fails to find the
To me it looks like you want server-forwarding, that is, you don't want
the client to know about server B.
This article discusses this more:
If my assumptions were wrong, please tell us what you have done, and what
"does not work" mean. We need a more informative error description.