Lab 15: Cisco Discovery Protocol

Lab Objective:

The objective of this lab exercise is for you to learn and understand how to enable CDP and adjust CDP timers.

Lab Purpose:

Understanding CDP is a fundamental skill. CDP is a proprietary Cisco protocol that can be used for device discovery as well as internetwork troubleshooting. As a Cisco engineer, as well as in the Cisco CCNA exam, you will be expected to know how to enable and use CDP in internetwork discovery and troubleshooting.

Certification Level:

This lab is suitable for CCENT and CCNA certification exam preparation.

Lab Difficulty:

This lab has a difficulty rating of 5/10.

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 10 minutes.

Lab Topology:

Please use the following topology to complete this lab:

Task 1:

Configure hostnames on R1 and Sw1 as illustrated in the topology.

Task 2:

Configure an IP address of 172.29.100.1/24 on R1 F0/0.

Task 3:

Configure VLAN200 on Sw1 and name it CDP_VLAN. Configure interface VLAN200 on Sw1 and assign it the IP address 172.29.100.2/24. Assign port FastEthernet0/2 on Sw1 to this VLAN.

Task 4:

Enable CDP on R1 and Sw1 globally (it’s already on by default but you can practice the command). Configure R1 and Sw1 to send CDP packets every 10 seconds. The timer command won’t work on Packet Tracer so use live equipment or GNS3.

Task 5:

Use CDP to see detailed information about Sw1 from R1. Familiarize yourself with the information provided.

Task 6:

Now disable CDP on the router interface and disable CDP globally on the switch.

Configuration and Verification

Task 1:

For reference information on configuring hostnames, please refer to earlier labs.

Task 2:

R1#conf t 
Enter configuration commands, one per line.  End with CTRL/Z. 
R1(config)#int fa0/0 
R1(config-if)#ip address 172.29.100.1 255.255.255.0 
R1(config-if)#no shut 
R1(config-if)#^Z 
R1#

Task 3:

Sw1#config t 
Enter configuration commands, one per line.  End with CTRL/Z. 
Sw1(config)#vlan200 
Sw1(config-vlan)#name CDP_VLAN 
Sw1(config-vlan)#exit 
Sw1(config)#interface vlan1 
Sw1(config-if)#shut 
Sw1(config-if)#exit 
Sw1(config)#int vlan200 
Sw1(config-if)#no shut 
Sw1(config-if)#ip address 172.29.100.2 255.255.255.0 
Sw1(config-if)#exit 
Sw1(config)#int f0/2 
Sw1(config-if)#switchport mode access 
Sw1(config-if)#switchport access vlan200 
Sw1(config-if)#end 
Sw1#ping 172.29.100.1

Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 172.29.100.1, timeout is 2 seconds: 
!!!!! 
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/203/1000 ms 
Sw1#

Task 4:

R1#conf t 
Enter configuration commands, one per line.  End with CTRL/Z. 
R1(config)#cdp run 
R1(config)#cdp timer 10 
R1(config)#^Z 
R1#show cdp interface fastethernet0/0 
FastEthernet0/0 is up, line protocol is up 
 Encapsulation ARPA 
 Sending CDP packets every 10 seconds 
 Holdtime is 180 seconds 

Sw1#conf t 
Enter configuration commands, one per line.  End with CTRL/Z. 
Sw1(config)#cdp run 
Sw1(config)#cdp timer 10 
Sw1(config)#end 
Sw1# 
Sw1#show cdp interface fastethernet0/2 
FastEthernet0/2 is up, line protocol is up 
 Encapsulation ARPA 
 Sending CDP packets every 10 seconds 
 Holdtime is 180 seconds

Task 5:

R1#show cdp neighbors detail 
-------------------------
Device ID: Sw1 
Entry address(es): 
 IP address: 172.29.100.2 
Platform: cisco WS-C2950G-24-EI,  Capabilities: Switch IGMP 
Interface: FastEthernet0/0,  Port ID (outgoing port): FastEthernet0/2 
Holdtime : 178 sec 

Version : 
Cisco Internetwork Operating System Software 
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(13)EA1, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2003 by cisco Systems, Inc. 
Compiled Tue 04-Mar-03 02:14 by yenanh 

advertisement version: 2 
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=00000000FFFFFFFF010221FF000000000000000DBD064100FF0000 
VTP Management Domain: “CISCO” 
Duplex: full

NOTE: The show cdp neighbors detail command provides detailed information about devices. This is a very useful troubleshooting command as you can find out the IP addresses (and more) of connected devices and access them remotely. Try this command on Sw1 and see the information you find out about on R1. Familiarize yourself with the contents of this command for both routers and switches.

Task 6:

R1#conf t 
Enter configuration commands, one per line.  End with CTRL/Z. 
R1(config)#int fa0/0 
R1(config-if)#no cdp enable 

Sw1(config)#no cdp run

NOTE: The CDP entries will still remain until they time out. You can clear the entries with the clear cdp table command, and then issue show commands to check that there are no entries. Knowing how to disable CDP is an important security task for the CCNA exam.


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