In general, the mac will get it's adress automatically assigned from
the router, if the router is using nat, (network address translation)
as most of them are. If you have a 192.168.x.x ip, then you're using
nat and cannot connect to your mac from remote. If you have most any
other address, then you're getting a real ip from the isp, and your
machine is directly addressable from the internet. There are other
address ranges that are used for private addressing, but 192.168 is
the most common.
