Type of device, IP address, and port number information.

Unanswered Question
Dec 21st, 2007

Is there a way to find out what is plugged into a switch. I need the IP address, Device type if possible, and port number it is in.

I found that the (show arp) will give me a list of IP addresses and mac addresses. But is it the mac addresses of the switch port or the device attached?

The (show mac-address-table) will give me ports with make addresses, but it show multiple address for some of the ports and I don't understand why?

The overall all thing I am trying to accomplish is putting devices into the correct vlans, but I don't want to accidentally remove a network printer and plug into a new vlan then users will have tons of problems. I would greatly appreciate any input you may have.

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Richard Burts Fri, 12/21/2007 - 06:09


Your post is not specific about whether the switch is a layer 2 switch or a layer2/3 switch. Be aware that the ARP table for a layer 2 switch will only show addresses that the management interface of the switch has accessed and not the entire content of devices connected to the switch.

The output of show arp will have the MAC address of the device attached and not the MAC of the switch port.

The show mac-address-table is the best way to view all devices and their MAC address that are reachable through this switch at layer 2. When it shows several MAC addresses on the same port it is an indication that this port is connected to another switch or to a hub and that several remote devices are reachable through this local port.

I am not aware of any command that will show device type of what is connected to the switch. The closest thing would be CDP but that only shows Cisco devices.



glynncounty Fri, 12/21/2007 - 06:13

I have both layer 2 and 3 switches I need to look at.. Using the show cdp neighbors I did see that there was a switch plugged into the port that was reporting mulitple addresses.

Anyway to tell what IP address is connected to what switch port?

Richard Burts Fri, 12/21/2007 - 06:22


There is not a simple and direct way to tell what IP address is connected to what switch port. On a layer 3 switch the ARP table should include all the end stations to which the switch has forwarded packets. On a layer 2 switch the ARP table only includes addresses which have been accessed by the switch, so you may need to ping the address from the switch to get the address into the ARP table. Then you can look at the ARP table to find the MAC address. Then you do a lookup in the mac-address-table and find the port where that MAC address is connected.




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