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Community Member

Identifying Switch Port by MAC and IP

I have this problem that I need a stepwise procedure for. We have this outsource support contract. They do not seem to understand Cisco products and I do not have access to the systems to figure this out myself. I have CCNA level experience (yet to take the test) but am a little rusty with a couple of years lag. I know that given an IP and a MAC you can find the port. The general network design though is obtrusive because most switches are not routed, they are daisy chained from one port to another. The majority are 5000/5500 series switches. This is what I know,

1. traceroute gets me to the core switches.

2. I need to get to the local switch the system is plugged into.

How do I step out of the core to the next switch?

1. show ip interface can show me where the packet is leaving the core based on information of the traceroute right?

2. show cdp neighbor should tell me the next switch in line towards the server, but it may be daisy chained off that switch to another 1 or 2 more switches.

3. Once I identify the switch it is on, I can use either show IP arp or show cam mac_addr to find the port it is connected to right?

Then I can once againt look at the interface to verify the mac and any errors as well as the duplex settings (which is what they were to verify and change). It took 21 hours before we got anywhere with this and I need to find a troubleshooting resolution until they can get their documentation of the network up to par.

4. Also, is there anything such as an arp ping or arp traceroute?



Cisco Employee

Re: Identifying Switch Port by MAC and IP

Steps to follow if you know the ip address of the endpoint you are looking for.

1. From a layer 3 device ping the endpoint

2. Check the arp table for the mac address of this endpoint

3. Use the show cam from one of your 5K's.

4. If the mac is learned off of a trunk port then use cdp neighbor to learn that switches IP address.

5. Repeat steps 3 and 4 until you get to the switch port that connects this endpoint.

This procedure, although perhaps not the best, will take a lot less time than 21 hours :)

Community Member

Re: Identifying Switch Port by MAC and IP

A utility named User Track included in Ciscoworks 2000 LMS can show you a table of 'mac_address - ip_address - port_id' and more, so you can find it out in a few seconds.

Community Member

Re: Identifying Switch Port by MAC and IP


If all your switches are running 6.x CatOS code then you can take advantage of l2trace utility. You can use the l2trace command to display the Layer 2 path taken by the packets that start at a specified source address and end at a specified destination address.

Refer this URL for command reference and usage guidelines:


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