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I am trying to find out the description of a particular interface in a 2950 Cisco switch, the interface has no description and I am trying to find out what device is connected to it. I've ran a couple of commands such as:

  • sh arp
  • sh mac address-table
  • sh cdp nei
  • sh cdp nei fa0/2 detail

but it does not show which device is connected to this interface.

  • What info do you actually want to see? Not all devices send information about themselves using CDP, but you should be able to see MAC address on an interface at least. – Alex Feb 21 '14 at 13:29
  • You have pretty much maxed out what information you can see about a host on a Cisco switch. The only other thing you could do is correlate your MAC address' to the OUI public listing. – Ryan Foley Feb 21 '14 at 13:40
  • @Fizzle I've figured it out no device is associated on that interface. I've used this sh mac address-table and checked each network device through its mac address. – chris Feb 21 '14 at 13:47
  • @chris If the interface is up|up and there is no MAC address associated with it, there is a good chance whatever is connected, isn't talking (thus, no ARP entry). – Ryan Foley Feb 21 '14 at 13:54
  • @Fizzle the interface is showing down | down through sh int status and sh int des, this switch only has two connected devices the uplink port and another one, I've checked the topology. – chris Feb 21 '14 at 13:59
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show arp should not help you as this device is a layer2 switch.

show cdp neigh should help you only if CDP is running on both this device and the other end

show mac address-table should help you, giving you at least one mac address seen on the other side of this link.

By trial and error you should be able to find the MAC address of the other side of the link in the mac address-table of this device. To get the mac address of an interface, use show interface.

While doing this, please document all the links, by doing a documentation you will never have to do this again. Easiest way is to track the cables.

Side note: I supposed the port is up/up.

Another trick you can use it to put the port in 10MBps and check the other switches for a 10MBps port. Or half duplex can be used also.

  • I figured it out nothing associated with that interface. – chris Feb 21 '14 at 13:43
  • SH ARP | INC IP address actually helps by locating the device through IP address. – chris Feb 21 '14 at 13:44

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