As described previously, routers use these addresses to decide whether to keep a packet in a local network or to forward it to a different network.
Addresses have four numeric fields.
For example, the address of the machine used by the Computational Science Education Project is 129.59.130.21. When you are using Internet software to communicate with another site, all you need to know about the site is its name. Most local networks either have a name server or a way to connect to a name server in order to translate symbolic names into internet addresses. If the translation fails, however, you can still make a connection by using the numeric address. For example, suppose you have an account on compsci , and you wish to log in.