Mobile TCP is a small program located in your Windows tray, the purpose of the program is to manage easy switching between networks when you are having a laptop or some other kind of dynamic IP switching (redundancy for example).
Most used for forwarding SMTP connections from your mail program to the right SMTP server, but you could forward any port type. Mobile TCP can also change your workgroup.
Everything depends on what network you are currently connected to.

Automatically checks the network status and detects changes, then by a set of IP/Mask rules Mobile TCP will select witch server to use.

Mobile TCP operates from the tray There is no nag screens, unwanted requesters or irritating sounds. Settings are straight forward. The uninstaller completely removes the program, its files and its registry entries, so do not feel afraid to try it.

Features:

Can check either external IP numbers (outside a firewall) or internal,
Forwards connections to the correct server,
Works silently in the background,
Easy to copy your current IP numbers to the clipboard,
Supports up to 10 simultaneous connections,
The Status window shows witch networks you have been connected to and when you sent e-mail,
Logfile option to save all the status messages,
Option to ignore the status of certain IP numbers,
Full in program documentation,
Checks for updates on the Internet,
Translation support,
Can change your workgroup depending on network.