Cisco Discovery Protocol (CDP)

Cisco discovery protocol is a layer 2 protocol (OSI) that operates between Cisco devices such as Router and switches. CDP displays information about the directly connected devices such as device ID, Platform, connected interface, IOS versions, and layer 3 IP address.

We use the network topology below as an example:

 

 

 Topology Configuration

 

HQ#config t

HQ(config)#interface fa0/0
HQ(config-if)#ip address 172.16.1.1 255.255.255.0
HQ(config-if)#no shutdown

HQ(config-if)#interface fa0/1
HQ(config-if)#ip address 200.199.90.1 255.255.255.0
HQ(config-if)#no shutdown
HQ(config)#interface se0/0/0
HQ(config-if)#ip address 172.16.2.2 255.255.255.252
HQ(config-if)#no shutdown
HQ(config)#interface se0/0/1
HQ(config-if)#ip address 192.168.1.2 255.255.255.252
HQ(config-if)#no shutdown
HQ(config)#router eigrp 100
HQ(config-router)#network 172.16.1.0
HQ(config-router)#network 172.16.2.0
HQ(config-router)#network 200.199.90.0.
HQ(config-router)#network 192.168.1.0

HQ(config-router)#no auto-summary

BRANCH1

BRANCH1#config t

BRANCH1(config)#interface fa0/0

BRANCH1(config-if)#ip address 172.16.3.1 255.255.255.0

BRANCH1(config-if)#no shutdown

BRANCH1(config)#interface se0/0/0

BRANCH1(config-if)#ip address 172.16.2.1 255.255.255.252

BRANCH1(config-if)#no shutdown

BRANCH1(config)#interface se0/0/1

BRANCH1(config-if)#ip address 192.168.3.1 255.255.255.252

BRANCH1(config-if)#no shutdown

BRANCH1(config)#router eigrp 100

BRANCH1(config-router)#network 172.16.3.0

BRANCH1(config-router)#network 172.16.2.0

BRANCH1(config-router)#network 192.168.3.0

BRANCH1(config-router)#no auto-summary

BRANCH2

BRANCH2#config t

BRANCH2(config)#interface fa0/0

BRANCH2(config-if)#ip address 192.168.2.1 255.255.255.0

BRANCH2(config-if)#no shutdown

BRANCH2(config)#interface se0/0/0

BRANCH2(config-if)#ip address 192.168.1.1 255.255.255.252

BRANCH2(config-if)#no shutdown

BRANCH2(config)#interface se0/0/1

BRANCH2(config-if)#ip address 192.168.3.2 255.255.255.252

BRANCH2(config-if)#no shutdown

BRANCH2(config)#router eigrp 100

BRANCH2(config-router)#network 192.168.1.0

BRANCH2(config-router)#network 192.168.2.0

BRANCH2(config-router)#network 192.168.3.0

BRANCH2(config-router)#no auto-summary  

 

How to use show command to examine CDP configuration. The table below lists and explains the various CDP commands output.

 

Show cdp	This displays the timer and version information
Show cdp ?	This displays a list of other cdp  commands
Show cdp interface	This displays timer information for all the interfaces on the router.
Show cdp interface fa0/0	This shows cdp information on fastEthernet 0/0 or other router interface
Show cdp neighbors	Displays a single line of information about directly connected neighboring device
Show cdp neighbors detail	The output shows detail information about all directly connected devices.
No cdp run	Disables cdp. You can find out if cdp is disabled by viewing the output on show cdp neighbor
No cdp enable	This command disables cdp on an interface. Firstly enter the interface configuration mode then use this command. This normal takes some time to take effect.

 

You can use Cisco Packet tracer for practice. dont forget to configure clock rates on serial interfaces and a routing protocol (EIGRP)

 

How to troubleshoot other Network Problems