31 - 238 CCNA 2: Routers and Routing Basics v3.1 Instructor Guide – Module 3 Copyright © 2004, Cisco Systems, Inc.
Ask students the following questions:
• Which command will show the configuration file in NVRAM?
• Which command will show the configuration file in RAM?
3.1.5 Configuring a serial interface A serial interface can be configured from the console or through a virtual terminal line. By
default, Cisco routers are DTE devices but they can be configured as DCE devices. 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 the DCE clock rate. Skip this step on DTE.
5. Turn on the interface.
There are two important items in this TI.
The first item is that setting a clock rate is not a normal configuration item. It is only done to
simulate a WAN. The clock is normally provided by the DCE equipment such as a CSU. The
curriculum shows the command entered as clock rate, but on some Cisco routers the
command can be entered as clockrate. Both will result in the same running configuration.
The second item is that interfaces are shutdown by default and must be enabled with the no
shutdown command. The shutdown command will turn off an interface. Instruct students to
check for interfaces that are shutdown when troubleshooting the student labs. This can be
checked by typing show interface serial 0/0 or show run int serial 0/0 for the
interface serial 0/0.
Ask students the following questions:
• What command turns on an interface?
• What command turns off an interface?
• What command is entered on an interface at the DCE end of the cable?
3.1.6 Making configuration changes To verify changes, use the show running-config command. This command will display
the current configuration. If the intended variables are not displayed, the environment can be
corrected in the following ways:
• Issue the no form of a configuration command.
• Restart the system and reload the original configuration file from NVRAM.