If your WWW browser is running on your local workstation and you
are not using a proxy, the display name probably is 18.220.140.5:0.
To find out what your display name really is, you can check what the
environment variable DISPLAY is set to (e.g. by running the
command echo $DISPLAY in a shell window).
If it is set to some brief name, like lips:0, you need to add
the domain name, probably cs.chalmers.se, before the colon,
to make it look more like 18.220.140.5:0.
If it is set to somethink like :0 or
:0.0,
you should add host before the colon.
The format of the display name is
host:number,
where host is the name of the host where the X server is running, and
number identifies which display/screen to use on that host. Usually,
number is 0.
When communicating within a local network, hosts can usually be specified
with a brief name, like lips. For communication between
arbitrary hosts on the Internet, you need to use full host names,
like 18.220.140.5.