NAT is a mechanism for conserving registered IP addresses in large networks and simplifying IP addressing management tasks. As a packet is routed through a network device, usually a firewall or border router, the source IP address is translated from a private internal network address to a routable public IP address. This allows the packet to be transported over public external networks, such as the Internet. The public address in the reply is then translated back to the private internal address for delivery within the internal network. A variation of NAT, called Port Address Translation (PAT), allows many internal private addresses to be translated using a single external public address.

Routers, servers, and other key devices on the network usually require a static IP configuration, which is entered manually. However, desktop clients do not require a specific address but rather any one in a range of addresses. This range is typically within an IP subnet. A workstation within a specific subnet can be assigned any address within a range while other values are static, including the subnet mask, default gateway, and DNS server.

The Dynamic Host Configuration Protocol (DHCP) was designed to assign IP addresses and other important network configuration information dynamically. Because desktop clients typically make up the bulk of network nodes, DHCP is an extremely useful timesaving tool for network administrators.

Students completing this module should be able to: