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chapter 3 ccna 4.15.4 Configuring the RouterThis chapter builds on the basic IOS configuration commands discussed in Chapter 10; Chapter 10 described how to switch between the various CLI modes and how to change device names, configure passwords, configure hardware parameters for interfaces, and enable interfaces. This section discusses these basic tasks as well as the commands dedicated to doing basic configuration of the router.15.4.1 Configuring InterfacesThis section first describes interface configurations not covered in Chapter 10, such as assigning IP addresses to interfaces and modifying bandwidth values, and then discusses some of the show commands used to verify interface configurations.IP Addressing InformationThere are many commands that can be used to configure IP addressing information on a router, one of the most common being the command to assign an IP address to an interface, but many others can be used, such as commands to configure DNS, restrict directed broadcasts, and perform other tasks. Some of these configurations are described later.Unlike a Layer 2 switch (such as a 2960 switch), which requires only an IP address for remote management, a router must have a unique IP address for each interface to which IP traffic is to be routed. In fact, each interface of the router belongs to a different network or subnet, so you must plan your IP addressing scheme properly by assigning a network number to each router segment and configuring the router interface with an unused host address in the corresponding segment. This address will become the default gateway for the devices connected to the interface. IP addresses and their components were discussed in Chapter 6.Consider two examples that assign correct and incorrect IP addresses to router interfaces. Figure 15.1 shows an example of an illegal configuration. In this example, only one network number is used: 192.168.1.0/24, and note that all of the router's interfaces are addressed from this network number. In fact, if you try to configure this addressing scheme on the router, you will get an address overlap error, which will prevent this configuration from being completed.Each interface requires a unique host address, as shown in Figure 15.2. In this example, the address for each interface comes from a different network number. Which host address to configure for a router interface depends on personal preference; many administrators use the first or last host address in the network to which the router interface belongs, but can use any unused valid host address in that network.As you may have guessed, to configure an IP address on a router, you must enter interface sub-configuration mode. Here is the syntax for configuring an IP address.