With my ADSL modem/router, it gets an IP address from my ISP using DHCP. I then connect to the internet by pointing my Linux and Windows setups to the modem/router's local address of 10.1.1.1.
I have my Linux set up to use a static IP address of 10.1.1.5, i.e. in my /etc/rc.d/rc.inet1.conf
# Config information for eth0:
Default gateway IP address:
In Windows, I ran the network connection wizard using the options to connect to the internet via another computer (i.e. the modem/router).
You may also need to specify a DNS name server if you use a setup like this.
In Linux, this is set in /etc/resolv.conf
where aaa.bbb.ccc.ddd is the IP address of your ISP's nameserver. This information can be supplied by your ISP, or may even be available by accessing your modem/router directly. In my case I can access the modem/router by opening a web browser and entering http://10.1.1.1
to get to a status page.
In Windows, it is set as an option under the Properties tab of the TCP/IP protocol settings in network connections.
I prefer this mode of operation as the modem/router has some useful features such as firewalling, URL blocking and port forwarding that I can utilise.