Small and Medium-Sized Enterprise Network Management: Cisco CDP protocol details

CDP: Cisco Discovery Protoco

Cisco Discovery protocol is a Cisco proprietary protocol used to discover adjacent contacts. All Cisco products support CDP. Unlike the routing protocol, the next hop target port is displayed for all known networks, CDP only displays directly connected neighbor information. CDP is very helpful in verifying whether a router is connected to an appropriate port of its neighbor.

Therefore, CDP aims to obtain information of directly adjacent devices.

It must be noted that only information of adjacent devices can be obtained. If the device is a remote device, other devices are separated, that is, cross-device information cannot be found, CDP does not work. You can use Telnet to obtain remote device information.

A vrocdp running CDP can learn the neighbor port and host name information directly connected to it. You can also obtain additional information about the neighbor's hardware mode number and its functions. Vrouters running CDP regularly broadcast packets with CDP update data. Use the cdp timer command to set the data update interval of CDP. The default value is 60 seconds. You can enable the cdp function by using cdp enable on a port. However, for security reasons, the CDP function is generally disabled in actual work.

CDP is a layer-2 protocol, so it can be transparent to network-layer protocols such as TCP/IP, regardless of what protocol stack other devices are running.

CDP protocol operation requirements physical description must support SNAP Protocol

The SubNetwork Access Protocol (SNAP) regulates the standard method for transmitting IP data packets over the IEEE802 network. That is to say, IP datagram can be encapsulated in 802.2LLC and then sent on the IEEE802 network.

Neighbor Information

On Cisco devices after CDP and IOS10.3, CDP can obtain the following information on features discovered by neighbors:

Device Host Name, address list, device capability, running software platform, Interface

 

Neighbor Information

Device ID indicates the Device name. If it is a vro or a host name, the MAC of the other Device is displayed.

Local Intrfce address list this is the interface of the Local device, that is, RB is connected to RA through Fas 0/0

Retention time of Holdtme Information

Capability is also called a role feature, such as a vro or a vswitch.

Platform, that is, the device model

Port ID.

If you want to obtain detailed information about the other party, run the command: show cdp entry *

 

CDP details

You can also use show cdp interface to display interface information.

 

Interface Information

You can also use show cdp traffic to display the traffic information with the other Party, including the number of CDP sent and received and the lending information.

CDP is enabled by default on Cisco devices. If CDP is enabled, we can run the command: no cdp run, disable or enable CDP on the routing interface and use cdp enable and no cdp enable ,:

 

Disable CDP

The above is a simple protocol about CDP, but it is often used in daily management work.

Conclusion: CDP is used to obtain information of directly adjacent devices. This protocol works in Layer 2. By default, a multicast notification is sent every 60 seconds at the address 01-00-0c-cc-cc-cc, if you do not receive notifications from the neighboring devices after reaching the 180-second holdtime limit, the information of the neighboring devices will be cleared.

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