question about urls and forums

[twoodcc]

i wasn't sure where to put this, so a mod can move it if need be.

so i have my own forum on my server, and it works great on my local network. but how can i get it to outside my network, and on it?

so, on my network, it's domain.local/forum (for example)

and i have my external is ex.ternal.net/forum

but this messes up my forum. the forum is set to domail.local/forum

but i can't go to ex.ternal.net/forum on my local network. so it looks to me that i can either have it work locally, or remotely, but not both.

is this possible?

thanks in advance