Category: Router Config

How to configure CDP – Cisco Discovery Protocol

In this article we will see how you can easilly configure and tune router CDP capabilities. If you are more interested in what CDP really means and how it works, visit “about CDP” article.

Cisco config

To see simple CD operation and use information that CDP can give you first thing to doo is learn how is possible to turn CDP on and off. If you, for example, want to list the summary information about what devices are connected to your router you can either selectively enable or disable Cisco Discovery Protocol on the entire router, or on individual interfaces. This is done by next couple of commands:

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Manage Router’s ARP Cache

Address Resolution Protocol (ARP) cache is a table where router or computer is keeping Layer 2 MAC addresses to Layer 3 IP addresses mappings which hw resolved lately. Without MAC to IP mapping the device would not be able to build and send IP packets.

Device discovers the MAC to IP mapping using ARP protocol Broadcast requests on the local subnet and saves the mapping in the ARP cache. If a device wants to send a packet to a neighbour, and it doesn’t have a corresponding MAC address, it sends out a broadcast ARP request packet. This broadcast packet reaches every device on the local subnet. Everybody will receive that ARP request packet but only the one device with the IP address mentioned in  ARP broadcast request packet responds back with an ARP response packet to complete the process.

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