If you configure the networking software on your host for standalone
operation (for instance, to be able to run the INN Netnews software),
you can safely skip this section, because the only IP address
you will need is for the loopback interface, which is always
127.0.0.1.
Things are a little more complicated with real networks like Ethernets.
If you want to connect your host to an existing network, you have to ask
its administrators to give you an IP address on this network. When
setting up a network all by yourself, you have to assign IP addresses
yourself.
Hosts within a local network should usually share addresses from the
same logical IP network. Hence, you have to assign an IP network address.
If you have several physical networks, you have to either assign them
different network numbers, or use subnetting to split your IP address
range into several subnetworks. Subnetting will be revisited in the
next section, Section 5.5.”
When picking an IP network number, much depends on whether you intend
to get on the Internet in the near future. If so, you should obtain an
official IP address now. Ask your network service
provider to help you. If you want to obtain a network number, just in
case you might get on the Internet someday, request a Network Address
Application Form from [email protected], or your
country's own Network Information Center, if there is one.
If your network is not connected to the Internet and won't be in the
near future, you are free to choose any legal network address. Just
make sure no packets from your internal network escape to the real
Internet. To make sure no harm can be done even if packets
did escape, you should use one of the network
numbers reserved for private use. The Internet Assigned Numbers
Authority (IANA) has set aside several network numbers from classes A,
B, and C that you can use without registering. These addresses are
valid only within your private network and are not routed between real
Internet sites. The numbers are defined by RFC 1597 and are listed in
Table 2-1 in Chapter 2. Note that the second and third blocks
contain 16 and 256 networks, respectively.
Picking your addresses from one of these network numbers is not
only useful for networks completely unconnected to the Internet; you can
still implement a slightly more restricted access using a single
host as a gateway. To your local network, the gateway is accessible by its
internal IP address, while the outside world knows it by an officially
registered address (assigned to you by your provider). We come back to
this concept in connection with the IP masquerade facility in
Chapter 11.
Throughout the remainder of the book, we will assume that the brewery's
network manager uses a class B network number, say
172.16.0.0. Of course, a class C
network number would definitely suffice to accommodate both the Brewery's and
the Winery's networks. We'll use a class B network here for the sake of
simplicity; it will make the subnetting examples in the next section
of this chapter a little more intuitive.
