Configuring a serial interface

Configuring a serial interface
3.1.5 This page will explain how a serial interface can be configured from the console or through a virtual terminal line. To configure a serial interface follow these steps:

1. Enter global configuration mode.
2. Enter interface mode.
3. Specify the interface address and subnet mask.
4. Set clock rate if a DCE cable is connected. Skip this step if a DTE cable is connected.
5. Turn on the interface.

Each connected serial interface must have an IP address and subnet mask to route IP packets. Configure the IP address with the following commands:

Router(config)#interface serial 0/0

Router(config-if)#ip address

Serial interfaces require a clock signal to control the timing of the communications. In most environments, a DCE device such as a CSU/DSU will provide the clock. By default, Cisco routers are DTE devices but they can be configured as DCE devices.

On serial links that are directly interconnected, as in a lab environment, one side must be considered a DCE and provide a clocking signal. The clock is enabled and speed is specified with the clock rate command. The available clock rates in bits per second are 1200, 2400, 9600, 19200, 38400, 56000, 64000, 72000, 125000, 148000, 500000, 800000, 1000000, 1300000, 2000000, or 4000000. Some bit rates might not be available on certain serial interfaces. This depends on the capacity of each interface.

By default, interfaces are turned off, or disabled. To turn on or enable an interface, the command no shutdown is entered. If an interface needs to be administratively disabled for maintenance or troubleshooting, the shutdown command used to turn off the interface.

In the lab environment, the clockrate setting that will be used is 56000. The commands that are used to set a clock rate and enable a serial interface are as follows:

Router(config)#interface serial 0/0
Router(config-if)#clock rate 56000
Router(config-if)#no shutdown

The next page will teach students how to change configurations.

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