Understanding Cisco Discovery Protocol (CDP)

Objective

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

Purpose

Understanding CDP is a fundamental skill. CDP is a proprietary Cisco protocol used for device discovery and 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.

Lab Topology

Use the following topology to complete this lab exercise:

Task 1: Configure Hostnames

Objective: Configure hostnames on R1 and SW1 as illustrated in the topology.

Configuration:

R1#conf t
Enter configuration commands, one per line. End with CTRL/Z.
R1(config)#hostname R1

SW1#conf t
Enter configuration commands, one per line. End with CTRL/Z.
SW1(config)#hostname SW1

Task 2: Configure IP Address on R1

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

Configuration:

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

Task 3: Configure VLAN200 on SW1

Objective: 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.

Configuration:

SW1#conf t
Enter configuration commands, one per line. End with CTRL/Z.
SW1(config)#vlan 200
SW1(config-vlan)#name CDP_VLAN
SW1(config-vlan)#exit
SW1(config)#interface vlan 1
SW1(config-if)#shut
SW1(config-if)#exit
SW1(config)#int vlan 200
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 vlan 200
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 80 percent (4/5), round-trip min/avg/max = 0/0/0 ms

Task 4: Enable and Configure CDP

Objective: 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.

Configuration:

R1#conf t
Enter configuration commands, one per line. End with CTRL/Z.
R1(config)#cdp run
R1(config)#cdp timer 10
R1(config)#exit
R1#show cdp interface fastethernet0/0
FastEthernet0/0 is up, line protocol is up
  Sending CDP packets every 60 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#show cdp interface fastethernet0/2
FastEthernet0/2 is up, line protocol is up
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds

Task 5: Use CDP for Device Information

Objective: Use CDP to see detailed information about SW1 from R1. Familiarize yourself with the information provided.

Configuration:

R1#show cdp neighbors detail

Device ID: SW1
Entry address(es):
  IP address : 172.29.100.2
Platform: cisco 2960, Capabilities: Switch
Interface: FastEthernet0/0, Port ID (outgoing port): FastEthernet0/2
Holdtime: 140

Version :
Cisco IOS Software, C2960 Software (C2960-LANBASEK9-M), Version 15.0(2)SE4, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2013 by Cisco Systems, Inc.
Compiled Wed 26-Jun-13 02:49 by mnguyen

advertisement version: 2
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: Disable CDP

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

Configuration:

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

SW1(config)#no cdp run
SW1(config)#end
SW1#copy running-config startup-config

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.

Cisco Packet Tracer file:
Load and open the .pkt Lab file in Cisco Packet Tracer from here: Cisco_Discovery_Protocol_CDP.pkt