|CCNA Cisco Certification boot camp.|
Cisco Discovery Protocol
Understanding How CDP Works
CDP is a media and protocol independent protocol that runs on all Cisco-manufactured equipment including routers, bridges, access and communication servers, and switches. Using CDP, you can view information about all the Cisco devices directly attached to the switch. In addition, CDP detects native VLAN and port duplex mismatches.
Network management applications can retrieve the device type and SNMP-agent address of neighboring Cisco devices using CDP. This enables applications to send SNMP queries to neighboring devices. CDP allows network management applications to discover Cisco devices that are neighbors of already known devices, in particular, neighbors running lower-layer, transparent protocols.
CDP runs on all media that support Subnetwork Access Protocol (SNAP), including LAN and Frame Relay. CDP runs over the Data Link layer only. Cisco devices never forward CDP packets. When new CDP information is received, Cisco devices discard old information.
Getting CDP Timer and Holdtime Information
The following command shows the CDP timer which is how often CDP packets are sent and the CDP holdtime which is the amount of time that the device will hold packets from neighbor devices.
Router_2#sho cdp Global CDP information: Sending CDP packets every 60 seconds Sending a holdtime value of 180 seconds
Setting the Holdtime and Timer
Use the following commands to set CDP timer and holdtime values.
Router_2#conf t Enter configuration commands, one per line. End with CNTL/Z. Router_2(config)#cdp timer 90 Router_2(config)#cdp holdtime 360
CDP can be disabled with the no cdp run command in global configuration mode (conf t).
Getting Neighbor Information
Because the router stores the CDP information in its cache memory, you can view it with a show command. It will only show information about directly connected devices since CDP packet aren't passed through the device.
Router_2#sho cdp neighbors 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 Router3 Ser 1 120 R 2500 Ser 0 Router1 Eth 1 180 R 2500 Eth 0 Switch1 Eth 0 240 S 1900 2CDP Neighbor Information includes
Show CDP Entry
The sho cdp entry [device id] command shows more information about the specified neighbor.
Router_2#sho cdp entry Router1 ------------------------- Device ID: Router1 Entry address(es): IP address: 192.168.1.2 Platform: cisco 2500, Capabilities: Router Interface: Ethernet1, Port ID (outgoing port): Ethernet0 Holdtime : 180 sec Version: Cisco Internetwork Operating System Software IOS (tm) 2500 Software (2500-JS-L), Version 11.2(15) RELEASED SOFTWARE (fcl) Copyright (c) 1986-1998 by Cisco Systems, Inc. Compiled Mon 06-Jul-98 22:22 by tmullins
Show CDP Neighbors Detail
The following is a sample output for one neighbor from the show cdp neighbors detail command. Additional detail is shown about neighbors, including network address, enabled protocols, and software version.
router#show cdp neighbors detail Device ID: 008024 1EEB00 (milan-sw-1-cat9k) Entry address(es): IP address: 18.104.22.168 Platform: CAT5000, Capabilities: Switch Interface: Ethernet1/0, Port ID (outgoing port): 2/7 Holdtime : 162 sec Version : Cisco Catalyst 5000 Duplex Mode: full Native VLAN: 42 VTP Management Domain: `Accounting Group'
Show CDP Traffic
The following example specifies information associated with the show cdp traffic command:
router# show cdp traffic Total packets output: 543, Input: 333 Hdr syntax: 0, Chksum error: 0, Encaps failed: 0 No memory: 0, Invalid: 0, Fragmented: 0 CDP version 1 advertisements output: 191, Input: 187 CDP version 2 advertisements output: 352, Input: 146
Show CDP Interface
To display information about the interfaces on which CDP is enabled, use the show cdp interface privileged EXEC command.Router#sh cdp interface [type number]
(Optional) Type of interface about which you want information.
(Optional) Number of the interface about which you want information.
Router_2#sho cdp interface Ethernet0 is up, line protocol is up Encapsulation ARPA Sending CDP packets every 60 seconds Holdtime is 180 seconds Serial0 is up, line protocol is up Encapsulation HDLC Sending CDP packets every 60 seconds Holdtime is 180 seconds Serial1 is up, line protocol is up Encapsulation HDLC Sending CDP packets every 60 seconds Holdtime is 180 seconds
Certification boot camp back to back.