Internet Connection Sharing (ICS) can be studied about on wikipedia. ICS isn't necessarily necessary.
Why avoid ICS (Internet Connection Sharing)
ICS, at least in Windows XP, cannot be turned off without reinstalling Windows from scratch, or possibly Repairing the OS. This means that once you enable it, you can't disable it. it will always be routing packets.
I have seen ICS cause networking trouble.
My best advice is, just avoid using it. find some other workaround - they exist. there are plenty of networking technologies around:
- switches (for dialup) that are cheaper than routers
- routers (for ethernet and cable/dsl/broadband)
- mobile broadband routers for sharing and routing/firewalling your mobile broadband dongle.
The only reason for having ICS
sharing dialup. but even then there are workarounds.
- use multiple NICs
- connect a switch
- plug an ethernet cable between the dialup computer and the switch
- plug another ethernet cable between the switch and the other computer and its NIC
- follow one of the bridging or network sharing ideas for multiple/2 NICs/wifi in the navigation on the left of this page. read any cautions first.