TCP/IP addresses

An IPv4 address is composed of four bytes, each of which has 8 bits and is called an octet. An example address is 140.88.76.22.

The decimal value of a byte can range from 0 to 255, which is the range of the values an octet can represent. Each octet is separated with a period and, depending upon the subnet mask used, you can break an IP address into a network and a host ID.

The subnet mask

The subnet mask is required for all IP configurations. Unlike the IP address, the mask address ranges from the largest number first. A subnet mask is often composed of either values of 255 or 0, although other values such as 24, 36, 92, 240, or 224 can be used. An example is 255.255.255.0.

Its appearance is different than the IP address and other parameters because it really isn't an address. Instead, it's a way to interpret IP addresses. Technically, a subnet mask defines bits that are used to compare the local IP address with the address of a node the local host wants to communicate with. The purpose of this comparison is to determine whether the other host is on the same local network.

Gateway

The default gateway specifies the address of the router connected to the local network. This router provides a path for packets destined for other networks. Packets destined for hosts on the local network can be sent directly to the host through the local network switch. Packets for remote hosts have the remote address included, but are sent directly to the router so it can determine the proper path to deliver them.

DNS

The DNS address specifies the IP address of the DNS server. The DNS server has a database that indexes computer names and IP addresses. When a user specifies a computer name, such as a Web site in a browser like www.google.com, DNS automatically resolves that name to an IP address so that communications can continue.