Note that you are not making any configuration changes, so you do not need access to enable mode. Router shows the MAC address's host is located through Port 5. There is a switch connected to port 5, so we run the command on the switch:. This shows the MAC address e. Congratulations, you have now found the offending host computer! Login Create Account Login.
Our company recently closed down half our office space, which was not being used. We gave back the unused space to the building management and had it walled off. Prior to us closing it off, I jotted down the network jack 's on the side to be closed and made sure to disconnect them from the switches in our server room. Today, I'm recreating a spreadsheet which lists all of our current physical network jacks, and where they are located in the resized office. For example, there is a logged in laptop plugged into jack So I go to the relay rack, find port 28, and trace it to the switch.
Problem is, the port that it's plugged into on the switch, is not lit up, showing it as inactive. But, it most definitely is active and on the network. Is there a way, either by IP or name, to query a Cisco switch to tell you which port that particular PC is plugged into? I guess my question is as above, is there a way to display the IP or name of whatever is attached to that port on the switch? Not quite a dupe, but there's a similar question here , which has some suggestions about mapping an IP address to a switch port.
How to Track Down a Switch Port
In this case, it sounds like the best option is to identify all switch ports that are connected to devices you know about. From your first hop router s , do a broadcast ping on each subnet that is trunked to a switch supporting the office space as opposed to any data centre space you may have. Note, this should be the directed broadcast address of each subnet, rather than the 'all devices' broadcast IP of For example, to ping all machines on the subnet This will populate the ARP cache of the router with entries for all machines on each subnet responding to ping.
You can check the list of IPs against DNS or another naming service to identify the names of specific devices.
- How to Track Down a Switch Port – Keller Schroeder;
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- On a Layer 2 switch:.
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Any IP address that you can't match a name to should be flagged for further investigation. Take the list of MAC addresses and use it to determine which switch port each device is connected to.
Note, the default time out for MAC address tables on Cisco devices is 5 minutes; you may need to run your broadcast ping again in order to repopulate it. For those IPs that you couldn't map to known devices, the commands in the previous section will tell you which port you need to check. Take the output, and remove the lines for any known MAC addresses, as well as any router-router and switch-switch links. The MAC addresses that you will be left with are devices that are connected to your switch, but aren't communicating via IP to your first hop routers.
Solved: Commands to find mac-address and IP on - Cisco Community
The ports these appear on should also be flagged for investigation. For all the ports you have flagged i. If you're lucky, your landlord will use managed cabling infrastructure ; if not, be prepared to lift floor tiles and trace cables the old fashioned way. Best of luck.
Accessing MAC address views and searches (Menu)
Use this command on the Cisco router's CLI:. Where xxxx. You may want to ping the broadcast IP to get everything to arp so devices that have been idle show up. CiscoWorks, or whatever they call it now, will definitely do this for you. In the example I have provided there were only 9 IP addresses. However in the real world there could be dozens or even hundreds of IP addresses. To help filter the results on a router type "show ip arp?
As stated in Step 4, you will likely have more than 9 IP Addresses.
This can be made worse in a messy closet with a 48 port switch running the closet and maybe even some layer 2 switches under that. Luckily in addition to being able to filter by interface you can also filter by VLAN. So type in "show ip arp? As you can see I typed in "sho ip arp vlan 20" and it listed only those IP's in vlan In this case it was the vlan interface and a PC. I hope this guide was helpful for you. If you aren't sure about something or feel like I missed a step, please let me know. Another way to find that information is to first PING the address of the system you are looking for.
- Accessing MAC address views and searches (Menu).
- Step 2: Find The MAC Addresses.
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Then issue: show arp i. As you can see, the 'sh arp' or 'sh ip arp' commands also give you the MAC addresses, so essentially the 'sh mac add' is only to get the port in which the device is connected. It helps to Ping the subnet's broadcast address e. Small tip: When you see a large number of MAC addresses showing up on a single port, there's a switch on that port into which those MAC addresses are connected. If you're all Cisco, 'show cdp neighbor' or 'sh cdp nei' will get you to the next switch.
The amazing thing to me is, this far into the 21st Century, this is still the only way I could find to get this information -- i. ETA: What if you can't get to the Console port? Good stuff, thanks for posting this! My go-to Cisco command is: show ip interface brief show ip int bri. Another thing I've learned that is very helpful I'm still a noob with Cisco stuff is tab-completion and using a "?
Unfortunately dumping the mac table and working through it is the only way to reliably find stuff and identify its switch port.