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The following sections describe these three reasons for planning and documentation and explain considerations for assigning private addresses within a network. There are many aspects of address planning and many different ways to allocate the addresses. For example, you can group your network addresses for hosts with different types of users. These sec-tions serve as a beginning point to introduce you to the planning process.

Preventing Duplication of Addresses

As you already know, each host in an internetwork must have a unique address. Without the proper planning and documentation of these network allocations, you could easily assign an address to more than one host. Duplicate addresses will impede the operation of the hosts.

Duplicate IP addresses will prevent the hosts trying to use the same address from communi-cating across the network. A duplicate IP address for a vital device on the network, such as an intermediary device or a server, can affect the operation of many other hosts.

Providing and Controlling Access

Some hosts, such as servers, provide resources to the internal network as well as to the external network. Access to these resources can be controlled by the Layer 3 address. If the addresses for these resources are not planned and documented, the security and accessibility of the devices are not easily controlled. For example, if a server has a random address assigned, blocking access to its address is difficult and clients might not be able to locate this resource.

Monitoring Security and Performance

Similarly, you will need to monitor the security and performance of the network hosts and the network as a whole. As part of the monitoring process, you examine network traffic, looking for addresses that are generating or receiving excessive packets. With the properly planned and documented network addressing, you can identify the device on the network that has a problematic address.

Assigning Addresses Within a Network

As you have already learned, hosts are associated with an IPv4 network by a common net-work portion of the address. Within a network, there are different types of hosts, such as the following:

■   End devices for users

■   Servers and peripherals

■   Hosts that are accessible from the Internet

■   Intermediary devices