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Embed code for: 12.9 Discovering Neighbors Using Cisco Discovery Protocol
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12.9 Discovering Neighbors Using Cisco Discovery Protocol
Discovering Neighbors Using Cisco Discovery Protocol Section 12: Configuring a Cisco Router You can enable or disable Cisco Discovery Protocol on a router as a whole (global) or on a portbyport (interface) basis and can view Cisco Discovery Protocol information with the show cdp command. Cisco Discovery Protocol has several keywords that enable access to different types of information and different levels of detail. The following example shows the different show cdp options. RouterA#show cdp ? entry Information for specific neighbor entry interface CDP interface status and configuration neighbors CDP neighbor entries traffic CDP statistics Cisco Discovery Protocol functionality is enabled by default on all interfaces (except for Frame Relay multipoint subinterfaces), but this functionality can be disabled at the device level. However, some interfaces, such as ATM interfaces, do not support Cisco Discovery Protocol. To prevent other Cisco Discovery Protocolcapable devices from accessing information about a specific device, the no cdp run global configuration command is used. To disable Cisco Discovery Protocol on an interface, the no cdp enable command is used. To enable Cisco Discovery Protocol on an interface, the cdp enable interface configuration command is used. RouterA(config)#no cdp run ! Disable CDP Globally RouterA(config)#interface serial0/0/0 RouterA(config-if)#no cdp enable ! Disable CDP on just this interface The show cdp neighbors command displays information about Cisco Discovery Protocol neighbors. The following example shows the Cisco Discovery Protocol output for RouterA. CDP Output for RouterA RouterA#show 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 SwitchA fa0/0 122 S I WS-C2960-fa0/2 RouterB s0/0/0 177 R S I 2811 s0/0/1 For each Cisco Discovery Protocol neighbor, the following information is displayed: Device ID Local interface Holdtime value, in seconds Device capability code Hardware platform Remote port ID The holdtime value indicates how long the receiving device should hold the Cisco Discovery Protocol packet before discarding it. The format of the show cdp neighbors output varies between different types of devices, but the available information is generally consistent across devices. The show cdp neighbors command can be used on a Cisco Catalyst switch to display the Cisco Discovery Protocol updates that are received on the local interfaces. Note that on a switch, the local interface is referred to as the local port. If you add the detail argument to the show cdp neighbors command, the resulting output includes additional information, such as the network layer addresses of neighboring devices. The output from the show cdp neighbors detail command is identical to that produced by the show cdp entry * command, as shown here. Device ID: RouterB Entry address(es): IP address: 10.1.1.2 Platform: Cisco 2811, Capabilities: Router Switch IGMP Interface: Serial0/0/0, Port ID (outgoing port): Serial0/0/1 Holdtime : 155 sec Version : Cisco IOS Software, 2800 Software (C2800NM-ADVIPSERVICESK9-M), Version 12.4(12), RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2006 by Cisco Systems, Inc. Compiled Fri 17-Nov-06 12:02 by prod_rel_team Cisco Discovery Protocol is limited to gathering information about directly connected Cisco neighbors. Other tools, such as Telnet, are available for gathering information about remote devices that are not directly connected. Content Unavailable This content is unavailable in this version of the course. Up Next: Troubleshooting Common Problems Associated with IP A…