Network Organization

Organizing your addressing becomes more problematic the bigger your network gets. If you have fewer than 254 devices needing an IP address, you're pretty much home free with a Class C network. But after that it can get interesting. There are some workarounds, though, which is what this section is about.

Subnetting

Class A and B networks can include separate networks called subnets. These subnets are specified in the second (in Class A networks) or third (Class B) octets. One computer with an address of 172.19.25.0 and another of 172.19.120.5 would be on the same Class B network (172.19), but on different subnets. These two computers would need a router or switch to communicate. Subnets can be useful to separate workgroups.

Netmasks

Subnet masks, or just plain netmasks, are used by TCP/IP to show which octets are owned by the network and which are owned by the host. You saw the standard netmasks earlier in the chapter. You can use customized netmasks to organize subnets to fit your needs. Even if you have a single Class C address, you can use netmasks to create subnets: Make that last octet a number greater than zero.

Network Address Translation (NAT)

NAT is a service that makes it possible for a server to translate between hosts on a network using private addresses and one or more public addresses. Usually, the router running NAT services all the clients on a network segment and shares a single registered IP address among all of them. This allows the hosts to essentially hide behind the router and a firewall is created at the network layer.