Cisco Systems CCNA 2 manual Disabling CDP, Troubleshooting CDP

If students have limited or no experience with the use of Telnet to move from device to device, this concept and skill should be reviewed. If students do not understand this capability, it will be difficult to understand the procedure described in this RIO. Demonstrate this capability if necessary. Refer to the figure to show students how telnet is used to map a network. Allow students to practice use of this command. Instruct students to map their router setup or a setup performed by another group.

4.1.5 Disabling CDP

Although CDP is enabled by default on all Cisco devices there may be situations in which CDP must be disabled. Three examples are included in the TI:

•If the bandwidth of a particular connection is inadequate, CDP can be disabled to conserve bandwidth.

•Since CDP is a Cisco proprietary device, if there is only one Cisco device on a network segment then there is no device with which to share information.

•If a particular device is connected to some other network such as an ISP, CDP can be disabled for security reasons. This will prevent the device from advertising information about itself to outside devices.

CDP can be disabled at two levels:

•The no cdp run command can be used in global configuration mode to disable CDP for the entire device. This should be used when only one Cisco device is present and CDP would serve no purpose on the network segment.

•CDP can be disabled for a specific interface. The network administrator must be in interface mode to perform this task. The command is no cdp enable or no cdp advertise-v2, based on the version of CDP that is used.

To determine if a particular interface has CDP enabled, the show cdp interface command can be used in user or privileged mode. The figures show the use of these commands.

Make sure students realize that CDP is enabled on all interfaces by default. Demonstrate how to disable CDP at the interface level and globally. Allow students to perform these commands on their own lab setup but ensure that students enable CDP when they are finished.

4.1.6 Troubleshooting CDP

CDP does not require any configuration. However there may be times when some of the following commands may be helpful in the troubleshooting process. A common problem may be devices with different versions of CDP. The show cdp neighbor command will show whether or not a device exists in the CDP neighbor cache and indicate if a device is utilizing version 2 of CDP.

43 - 238 CCNA 2: Routers and Routing Basics v3.1 Instructor Guide – Module 4 Copyright ♥ 2004, Cisco Systems, Inc.