Before you can configure TCP/IP, you need to determine the following information about your network setup. In most cases, your local network administrator can provide you with this information.
If you're only configuring loopback mode (i.e. no SLIP, no ethernet card, just TCP/IP connections to your own machine) then your IP address is 127.0.0.1.
Your network administrators will have chosen the netmask when the network was designed, and therefore they should be able to supply you with the correct mask to use. Most networks are class C subnetworks which use 255.255.255.0 as their netmask. Other Class B networks use 255.255.0.0. The NET-2 code will automatically select a mask that assumes no subnetting as a default if you do not specify one.
This applies as well to the loopback port. Since the loopback port's address is always 127.0.0.1, the netmask for this port is always 255.0.0.0. You can either specify this explicitly or rely on the default mask.
If you're only using loopback, you don't have a network address.
For example, if your IP address is 184.108.40.206, and your netmask is 255.255.255.0, your broadcast address is 220.127.116.11.
Note that for historical reasons, some networks are setup to use the network address as the broadcast address, if you have any doubt, check with your network administrators. (In many cases, it will suffice to duplicate the network configuration of other machines on your subnet, substituting your own IP address, of course.)
If you're only using loopback, you don't have a broadcast address.
In fact, you may have multiple gateways. A gateway is simply a machine that lives on two different networks (has IP addresses on different subnets), and routes packets between them. Many networks have a single gateway to ``the outside world'' (the network directly adjacent to your own), but in some cases you will have multiple gateways---one for each adjacent network.
If you're only using loopback, you don't have a gateway address. The same is true if your network is isolated from all others.
If you're only using loopback, you don't have a nameserver address.
SLIP users: You may or may not require any of the above information, except for a nameserver address. When using SLIP, your IP address is usually determined in one of two ways: Either (a) you have a ``static'' IP address, which is the same every time you connect to the network, or (b) you have a ``dynamic'' IP address, which is allocated from a pool available addresses when you connect to the server. In the following section on SLIP configuration this is covered in more detail.
NET-2 supports full routing, multiple routes, subnetworking (at this stage on byte boundaries only), the whole nine yards. The above describes most basic TCP/IP configurations. Yours may be quite different: when in doubt, consult your local network gurus and check out the man pages for route and ifconfig. Configuring TCP/IP networks is very much beyond the scope of this book; the above should be enough to get most people started.