Guest access by IP

[iceblock]

I've been searching and I don't think there's anything about this.

The forum I'm working on is part of the Intranet but available on the Internet. If it's access from internal network, guest access is allowed. If it's accessed via external network, login is required.

Are there any mods that ban or allow access for a range of IPs? Or where can I hack the code to do this before a mod is available?