At work I've been tasked to create a program that acts similar to Fluke testing devices (such as LinkRunners) but will be much more extensive and specific to our needs. One of the capabilities that has been requested is determining the interface port that the testing device is currently connected to.

So before I run off into detail, does Cisco deploy a standard or proprietary protocol that handles all this? Somehow a Fluke LinkRunner is retrieving the information without logging in administratively, an operation that I would like to mimic.

To put this in perspective, a laptop with the loaded software will either connect directly to an Ethernet port on the switch or through permalink by testing on the jack-end where it is terminated for the customer. Like Fluke testing devices they would like for it to display the switch name, interface, port, VLAN, etc. so that the technician may verify that everything is working properly.

What I don't know (since I'm only a student engineer being trained on the job) is how Cisco communicates with a testing device and provides this information. I understand that you can determine what a device is connected to on the administrative end by checking for the MAC Address in the ARP table or looking up the client IP but this is to work on the front-end. I could try to use SNMP but with how the college has set up the network the switches are on a different, secure VLAN. The laptop would not be able to jump onto this VLAN to run SNMP and fetch the required information.

Ideas, suggestions, questions, critcism?


CDP/LLDP was pointed out and I feel silly for working with these but not having had yet researched them. From this I can get information, however this brings up another question if it must be enabled on the switch to allow retrieving said information.

A comment upon the answer has finished fulfilling my questions. Special thanks to the two who helped!

1 Answer 1


I'm almost 100% positive that for Cisco switches it would be CDP (Cisco Discovery Protocol) while on other vendors, they would use the industry standard LLDP (Link Layer Discovery Protocol). From CDP, you can get information such as switch port, VLAN, switch name, and link negotiation info (e.g. full vs half duplex) to name a few.

I hope this helps.

  • It does! I just read a bit more on CDP and LLDP actually. I feel real silly for not having read up more on these two. However, does CDP/LLDP need to be enabled switch-side? I'm restricted up to Layer 2 and do not have privileges to enable it on switches (but I can on ports) Feb 24, 2015 at 16:40
  • 1
    CDP needs to be enabled on all equipment you'd like to see connected when running the command: show cdp neighbors. If a switch doesn't have CDP it will not show up when that command is run.
    – HAL
    Feb 24, 2015 at 17:11
  • @HAL Thanks HAL! I believe most of our equipment has CDP enabled but not LLDP. I think I have enough now to get started Feb 24, 2015 at 17:30
  • Yes, CDP can be enabled/disabled globally and individually on each switch port. So it will at the very least need to be enabled globally in order to allow your changes at the port level to work. Feb 24, 2015 at 18:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.