Cisco Ccna Exam Tutorial Cisco Discovery Protocol Cdp

Cisco Ccna Exam Tutorial Cisco Discovery Protocol Cdp

Cisco CCNA Exam Tutorial: Cisco Discovery Protocol (CDP)
The Cisco Discovery Protocol (CDP) sure looks simple enough, but there are quite a​ few details to​ know for​ success on​ the CCNA exam .​
in​ your​ CCNP studies, you'll be introduced to​ additional uses for​ CDP, but for​ now it's enough to​ know that CDP is​ designed to​ give you​ information​ regarding directly connected Cisco routers and​ switches.
CDP runs by default between all directly connected Cisco devices .​
CDP is​ also a​ Cisco-proprietary protocol - if​ the directly connected device is​ not a​ Cisco device, you​ won't see the information​ you​ wanted.
The basic CDP command​ to​ display information​ about the directly connected neighbor is​ show cdp neighbor.
R2#show cdp neighbor
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I​ - IGMP, r – Repeater

Device ID Local Intrfce Holdtme Capability Platform Port ID
R1 BRI0 167 R 2521 Dialer1
this​ command​ is​ particularly helpful when troubleshooting Cisco switches .​
There’s no need to​ trace wiring in​ a​ rack of​ Cisco devices to​ see what routers are connected to​ a​ Cisco switch when show cdp neighbor can be used .​
in​ the above output, you​ can see the remote device's hostname, what interface on​ the remote device is​ connected to​ the local device, the capability of​ the remote device, the remote device’s hardware platform, and​ the local interface that is​ connected to​ the remote device.
CDP can be disabled at​ both the global and​ interface level .​
To disable CDP at​ the interface level, run no cdp enable on​ the interface, and​ cdp enable to​ turn it​ back on​ .​

cdp timer defines how often CDP packets are transmitted, and​ cdp holdtime defines how long a​ device will hold a​ received packet.
To turn CDP off for​ the entire router, run no cdp run .​
To view the current global status of​ CDP, run show cdp .​
R2#show cdp
Global CDP information:
Sending CDP packets every 60 seconds
Sending a​ holdtime value of​ 180 seconds

CDP is​ running by default.

R2#conf t
R2(config)#cdp timer 45
R2(config)#cdp holdtime 100

The CDP timers are changed.

R2#show cdp
Global CDP information:
Sending CDP packets every 45 seconds
Sending a​ holdtime value of​ 100 seconds
The CDP values have been successfully changed .​
show cdp interface will give the timer information​ for​ each interface on​ the router.
R2#conf t
R2(config)#interface bri0
R2(config-if)#no cdp enable

CDP is​ disabled on​ the BRI interface .​
this​ does NOT have to​ be done to​ keep the line from dialing.

R2#conf t
R2(config)#no cdp run

CDP is​ disabled globally.

R2#show cdp
% CDP is​ not enabled
CDP has been successfully disabled.
Show cdp neighbor gives you​ a​ great deal of​ information, but what if​ you​ need the neighbor’s IP address? Just run show cdp neighbor detail .​
you​ will get even more information​ about that directly connected neighbor, including its IP address.
SW2#show cdp neighbor detail
Device ID: R4
Entry address(es):
IP address:
Platform: cisco 2520, Capabilities: Router
Interface: FastEthernet0/4, Port ID (outgoing port): Ethernet0
Holdtime : 158 sec
The details of​ CDP are important to​ you​ on​ the job and​ in​ the CCNA exam room .​
When you​ find yourself negotiating a​ badly documented network, you​ can use CDP to​ walk through the network and​ create a​ network map for​ your​ client as​ well .​
Sometimes the simplest protocols are the most helpful!

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