Summary

Summary

This page summarizes the topics discussed in this module.

CDP is used to obtain information about directly connected Cisco devices. This includes the router interfaces the devices are connected to, the interfaces used to make the connections, and the model numbers of the devices. CDP is media and protocol independent, and runs on all Cisco equipment over SNAP. It is a Layer 2 protocol that connects lower physical media and upper network layer protocols.

When a Cisco device boots up, CDP starts up automatically and allows the device to detect directly connected Cisco devices that also use CDP. It operates at the data link layer and allows two systems to learn about each other, even if they use different network layer protocols. The show cdp neighbors command is used to display information about the networks that are directly connected to a router.

The cdp run command is used to enable CDP globally on a router. The cdp enable command is used to enable CDP on a particular interface. To disable CDP at the global level, use the no cdp run command in global configuration mode.

The telnet command may be run from the user or privileged EXEC mode. It allows a user to remotely access another device. It is not necessary to enter the command connect or telnet to establish a Telnet connection. To end a Telnet session, use the exit or logout commands. Once the Telnet session is completed, log off the host. The Telnet connection will terminate after ten minutes of inactivity by default or when the exit command is entered at the user or privileged EXEC prompt.

Other connectivity tests include ping and traceroute. The ping command sends a packet to the destination host and then waits for a reply packet from that host. Results from this echo protocol can help determine the path-to-host reliability, delays over the path, and if the host can be reached or is functional. The traceroute command is similar to the ping command, except that instead of testing end-to-end connectivity, traceroute tests each step along the way. This operation can be performed at either the user or privileged EXEC levels.