Table of Contents
Cisco Discovery Protocol
These blog posts I created to help me as a reference tool, as well as a way of retaining the knowledge. If you find it useful that’s just a plus.
Configuration Commands
CDP Enable
Enables CDP on an interface. The command can be used in both the global and interface configuration modes. The no form of the command disables CDP on the interface.
Syntax:
cdp enable
no cdp enable
Example:
Router1>enable
Router1#configure terminal
Router1(config)#interface GigabitEthernet0/1
Router1(config-if)#cdp enable
CDP Holdtime
Specifies or modifies the time (in seconds) that the receiving device should hold a CDP packet before discarding it.
Syntax:
cdp holdtime 180
Example:
Router1>enable
Router1#configure terminal
Router1(config)#interface GigabitEthernet0/1
Router1(config-if)#cdp enable
Router1(config-if)#cdp holdtime 180
CDP Timer
Configures how often the Cisco IOS software sends CDP packets.
Syntax:
cdp timer 60
Example:
Router1>enable
Router1#configure terminal
Router1(config)#interface GigabitEthernet0/1
Router1(config-if)#cdp enable
Router1(config-if)#cdp timer 30
Display Commands
Show CDP
Displays global CDP information, including timer and hold-time settings.
Syntax:
show cdp
Example:
Router1>enable
Router1#show cdp
Show CDP Entry
Displays detailed information about a specific neighboring device using CDP.
Syntax:
show cdp entry *
show cdp entry {entry-name} [protocol | version]
Example:
Router1>enable
Router1#show cdp entry SwitchA
Show CDP Interface
Displays information about interfaces on which CDP is enabled.
Syntax:
show cdp interface [interface]
Example:
Router1>enable
Router1#show cdp interface GigabitEthernet0/1
Show CDP Neighbors
Displays information about directly connected neighbors.
Syntax:
show cdp neighbors
Example:
Router1>enable
Router1#show cdp neighbors
Show CDP Detail
Provides detailed information about connected neighbors, including device types, interface names, and IP addresses.
Syntax:
show cdp neighbors detail
Example:
Router1>enable
Router1#show cdp neighbors detail
Show CDP Traffic
Displays information about traffic between devices gathered by using CDP.
Syntax:
show cdp traffic
Example:
Router1>enable
Router1#show cdp traffic
EVE-NG Lab
In this EVE-NG lab, I used a simple topology involving three routers (Router1, Router2, and Router3) connected via serial interfaces. This lab will guide you through configuring each router with the appropriate IP settings, enabling CDP, and verifying that CDP is functioning correctly.
| Device | Interface | IP Address | Subnet Mask |
|---|---|---|---|
|
Router1 |
S0/0/0 |
10.1.1.1 |
255.255.255.0 |
|
Router2 |
S0/0/0 |
10.1.1.2 |
255.255.255.0 |
|
Router2 |
S0/0/1 |
172.16.10.2 |
255.255.255.0 |
|
Router3 |
S0/0/0 |
172.16.10.1 |
255.255.255.0 |
Configuring IP Addresses
Router1
Enter global configuration mode:
Router1>enable
Router1#configure terminal
Configure the IP address for S0/0/0 interface:
Router1(config)# interface Serial 0/0/0
Router1(config-if)# ip address 10.1.1.1 255.255.255.0
Router1(config-if)# no shutdown
Exit the interface configuration mode:
Router1(config-if)# exit
Router2
Enter global configuration mode:
Router2>enable
Router2#configure terminal
Configure the IP address for S0/0/0 interface:
Router2(config)# interface Serial 0/0/0
Router2(config-if)# ip address 10.1.1.2 255.255.255.0
Router2(config-if)# no shutdown
Configure the IP address for S0/0/1 interface:
Router2(config)# interface Serial 0/0/1
Router2(config-if)# ip address 172.16.10.2 255.255.255.0
Router2(config-if)# no shutdown
Exit the interface configuration mode:
Router2(config-if)# exit
Router3
Enter global configuration mode:
Router3>enable
Router3#configure terminal
Configure the IP address for S0/0/0 interface:
Router3(config)# interface Serial 0/0/0
Router3(config-if)# ip address 172.16.10.1 255.255.255.0
Router3(config-if)# no shutdown
Exit the interface configuration mode:
Router3(config-if)# exit
Enabling CDP
All Routers
CDP is enabled by default on Cisco routers. However, if it has been disabled, you can re-enable it:
Router>enable
Router#configure terminal
Router(config)#cdp run
Verify that CDP is enabled on each interface:
Router>enable
Router#show cdp interfaces
Verify CDP Configuration
All Routers
After enabling CDP, you can verify the configuration and check for neighboring devices:
Router>enable
Router#show cdp neighbors
Display detailed information:
Router>enable
Router#show cdp neighbors detail