Objective: Learn how the Cisco Discovery Protocol (CDP) functions and what is required for Cisco devices to be discovered.
Lab Equipment: Router 1 and Router 4 from the eRouters menu
Background Reading: Lab Primer Lesson 5: CDP
1. On Router 1, enter global configuration mode.
Router>enable
Router#conf t
Router(config)#
Lab Equipment: Router 1 and Router 4 from the eRouters menu
Background Reading: Lab Primer Lesson 5: CDP
1. On Router 1, enter global configuration mode.
Router>enable
Router#conf t
Router(config)#
2. Change the host name to R1.
Router(config)#hostname R1
R1(config)#
3. Connect to Router 4, and change the host name to R4.
Router>enable
Router#conf t
Router(config)#hostname R4
R4(config)#
4. Return to R1, and enable the serial 0 interface. By default, all interfaces are shut down(disabled).
R1(config)#interface serial 0
R1(config-if)#no shutdown
5. Now, enable the serial 0 interface on R4.
R4(config)#interface serial 0
R4(config-if)#no shutdown
6. Enable the Ethernet 0 interface on R1.
R1(config)#interface Ethernet 0
R1(config-if)#no shutdown
R1(config)#interface Ethernet 0
R1(config-if)#no shutdown
7. CDP allows devices to share basic configuration information and will operate without any protocol-specific information being configured. CDP, which is enabled by default on all interfaces, is a Data Link protocol that operates at Layer 2 of the OSI model. This is important to understand because CDP is not routable; it can only travel to directly connected devices.On R1, type the command that displays the status of all interfaces that are running CDP.
R1(config-if)#exit
R1(config)#exit
R1#show cdp interface
The sample output below shows that both interfaces are up and sending CDP packets:Serial0 is up, line protocol is up
Encapsulation HDLC
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
<output omitted>
R1#
Now that the router has interfaces that are broadcasting and receiving CDP updates,you can use CDP to find out about directly connected neighbors.
Encapsulation HDLC
Sending CDP packets every 60 seconds
Holdtime is 180 seconds
<output omitted>
R1#
Now that the router has interfaces that are broadcasting and receiving CDP updates,you can use CDP to find out about directly connected neighbors.
8. On R1, type the command that provides information about directly connected neighbors.
R1#show cdp neighbors
Below is some sample output:
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Interface Holdtime Capability Platform Port ID
R4 Serial 0 172 R 2501 Serial 0
R1#
The first device on the directly connected neighbors list for R1 is R4 via the serial 0 link. R1 is receiving CDP updates from R4; the updates tell R1 to retain the information for a specified amount of time. At the time this command was entered, there were 172 seconds left in the hold time for R1’s update. If that time expires before another update is received, R1’s information will be removed from the table. R4 is a 2000 series router,as indicated in the Platform column. The final column, Port ID, indicates the port on the other device from which the updates are being sent.
9. On R1, type the command that provides more detailed information about directly connected neighbors.
R1#show cdp neighbor detail
Below is some sample output:
Device ID: R4
Entry address(es):
Platform: cisco 2501, Capabilities: Router
Interface: Serial0, Port ID (outgoing port): Serial0
Holdtime : 162 sec
Version:
Cisco Internetwork Operating System Software
Software, Version 12.0(16), RELEASE SOFTWARE (fc2)
Copyright (c) 1986-2001 by cisco Systems, Inc.
Compiled Fri 02-Mar-01 17:34 by dchih
The show cdp neighbor detail command shows devices one at a time. It is used to display Network layer address information. The command also displays IOS version information. Notice that the devices are listed in order. If you wanted to find out information about a device further down the list, you would need to scroll down using the SPACEBAR.
Interface: Serial0, Port ID (outgoing port): Serial0
Holdtime : 162 sec
Version:
Cisco Internetwork Operating System Software
Software, Version 12.0(16), RELEASE SOFTWARE (fc2)
Copyright (c) 1986-2001 by cisco Systems, Inc.
Compiled Fri 02-Mar-01 17:34 by dchih
The show cdp neighbor detail command shows devices one at a time. It is used to display Network layer address information. The command also displays IOS version information. Notice that the devices are listed in order. If you wanted to find out information about a device further down the list, you would need to scroll down using the SPACEBAR.
10. On R1, type the command to provide information about the specific device R4.
R1#show cdp entry R4
The show cdp entry command provides the same information as the show cdp neighbor detail command, but it allows a single device to be specified. Also, notice that this is one of the only case-sensitive commands that exist.
11. On R1, type the command that shows how often CDP updates are being sent and how long a recipient should retain the update.
R1#show cdp
12. On R1, adjust the number of seconds between CDP updates to 45.
R1#conf t
R1(config)#cdp timer 45
R1#conf t
R1(config)#cdp timer 45
Besides the update interval, the holdtime value may also be adjusted. This value tells the recipient of the update how long to retain the CDP information in the update. It is also a global parameter.
13. On R1, type the command to adjust the holddown timer to 60 seconds.
R1#conf t
R1(config)#cdp holdtime 60
14. On R1, type the command that will allow you to verify that the changes have been made.
R1#show cdp
15. If there are no other directly connected Cisco devices on the network, or if you want to conserve bandwidth, you can disable CDP.On R1, type the command that disables CDP for the entire router.
R1#conf t
R1(config)#no cdp run
At times, you may wish to disable CDP for a specific interface for security reasons, or simply because the interface has very low bandwidth.
16. On R1, type the command that turns CDP back on for the entire router.
R1#conf t
R1(config)#cdp run
17. On R1, disable CDP for only the specific interface Ethernet 0.
R1(config)#interface Ethernet 0
R1(config-if)#no cdp enable
18. On R1, verify that Ethernet 0 is no longer sending CDP updates. (If the Ethernet 0 interface does not show up as an entry in the output, you can conclude that it is not sending CDP updates.)
R1#show cdp interface
Below is sample output from the command:
R1#show cdp interface
Serial0 is up, line protocol is up
Encapsulation HDLC
Sending CDP packets every 45 seconds
Holdtime is 60 seconds
**********************************************
本文转自redking51CTO博客，原文链接：http://blog.51cto.com/redking/69916
，如需转载请自行联系原作者
