Cisco Systems RJ-45-to-AUX Show cam, Duplicate MAC Addresses, Show cdp neighbors, Show config

∙show cam

∙show cdp neighbors

∙show config

∙show flash

∙show interface

∙show log

∙show mac

∙show port

∙show spantree

∙show system

∙show test

∙show version

∙show vtp domain controller

show cam

The show cam command displays a switch’s transparent bridging table (also known as the Content Addressable Memory [CAM] table). This is a table of the Layer 2 MAC addresses attached to each port that the switch has learned in order to make forwarding decisions.

Duplicate MAC Addresses

Occasionally, because of production mistakes, network devices are configured with identical MAC addresses on their interfaces. There are also some dual−homed Unix workstations that use manually assigned MAC addresses. This is a situation that leaves the door wide open for a duplicate MAC address in the network. This in turn can prevent communication in the local network. When the devices with the same MAC address are on the same broadcast domain, duplicate MAC addresses can become a substantial problem in your network.

By using the show cam command, you can view the list of known MAC addresses for interfaces attached to each switch port. If you are in a network where the administration of network devices is divided within the organization, I recommend that a central process be created to review and document assigned MAC addresses and thereby avoid this duplication problem.

Note On the Cisco CLI−based IOS, use the show mac command.

show cdp neighbors

Cisco Discovery Protocol (CDP) is a Cisco proprietary protocol used to discover neighboring Cisco devices. The show cdp neighbors command displays the hardware, IOS version, and active interfaces. This information is passed between Cisco devices by CDP packets on physical media that support SNAP.

CDP packets are multicast packets that are advertised by the Cisco router or switches but not forwarded. This protocol is available on the Cisco IOS version 10.3 and later. You can use the show cdp neighbors command on both the CLI and Set/Clear command−based IOS.

show config

The show config command displays an incredible amount of troubleshooting information. With this command, you can obtain the entire configuration of switches and modules (except the Route Switch Module [RSM]) including passwords, system information, protocol settings, interface settings, and the system log settings.

Note On the CLI−based IOS, use the show running−config command.

314