The show cdp neighbors Command

In this article we will discuss The show cdp neighbors Command , will make brief discussion on CDP Command, In last article we discuss about The arp Command.

There are several other IOS commands that are useful. For example, the Cisco Discovery Protocol (CDP) is a Cisco-proprietary protocol that runs at the data link layer. Because CDP operates at the data link layer, two or more Cisco network devices, such as routers that support different network layer protocols, can learn about each other even if Layer 3 connectivity does not exist.

When a Cisco device boots, CDP starts by default. CDP automatically discovers neighboring Cisco devices running CDP, regardless of which Layer 3 protocol or suites are running. CDP exchanges hardware and software device information with its directly connected CDP neighbors.

CDP provides the following information about each CDP neighbor device:

  • Device identifiers – For example, the configured host name of a switch
  • Address list – Up to one network layer address for each protocol supported
  • Port identifier – The name of the local and remote port in the form of an ASCII character string, such as FastEthernet 0/0
  • Capabilities list – For example, whether this device is a router or a switch
  • Platform – The hardware platform of the device; for example, a Cisco 1841 series router

The show cdp neighbors detail command reveals the IP address of a neighboring device. CDP will reveal the neighbor’s IP address regardless of whether or not you can ping that neighbor. This command is very helpful when two Cisco routers cannot route across their shared data link. The show cdp neighbors detailcommand will help determine if one of the CDP neighbors has an IP configuration error.

As helpful as CDP is, it can also be a security risk because it can provide useful network infrastructure information to attackers. For example, by default many IOS versions send CDP advertisements out all enabled ports. However, best practices suggest that CDP should be enabled only on interfaces that are connecting to other infrastructure Cisco devices. CDP advertisements should be disabled on user-facing ports.

Because some IOS versions send out CDP advertisements by default, it is important to know how to disable CDP. To disable CDP globally, use the global configuration command no cdp run. To disable CDP on an interface, use the interface command no cdp enable.

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