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Each of these different device types should be allocated to a logical block of addresses within the address range of the network. An important part of planning an IPv4 addressing scheme is deciding when private addresses are to be used and where they are to be applied. Considerations include the following:

■   Will there be more devices connected to the network than public addresses allocated by the network ISP?

■   Will the devices need to be accessed from outside the local network?

■   If devices that can be assigned private addresses require access to the Internet, is the network capable of providing a Network Address Translation (NAT) service?

If there are more devices than available public addresses, only those devices that will direct-ly access the Internet, such as web servers, require a public address. A NAT service would allow those devices with private addresses to effectively share the remaining public addresses.

Static or Dynamic Addressing for End-User Devices

Addresses in the network can be assigned to hosts statically or dynamically. The decision whether to use static or dynamic assignment for a particular device depends on several fac-tors described in the following sections.

Addresses for User Devices

In most data networks, the largest population of hosts includes the end devices such as PCs, IP phones, printers, and PDAs. Because this population represents the largest number of devices within a network, the largest number of addresses should be allocated to these hosts. IP addresses can be assigned either statically or dynamically.

Static Assignment of Addresses

With a static assignment, the network administrator must manually configure the network information for a host. At a minimum, this includes entering the host IP address, subnet mask, and default gateway. Static addresses for the interface of a Windows-based computer can be set in the IP Properties screen for the network interface, as shown in Figure 6-11.

Static addresses have some advantages over dynamic addresses. For example, they are use-ful for printers, servers, and other networking devices that need to be accessible to clients on the network. If hosts normally access a server at a particular IP address, it would cause problems if that address changed. Additionally, static assignment of addressing information can provide increased control of network resources. However, it can be time consuming to enter the information on each host.