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I am interested in finding the IP addresses assigned to devices attached to each interface on a Cisco 2960X switch. It seems like IPDT is exactly what I'm looking for. However it seems like the refresh interval is a bit odd.

The way I understand it:

  • IPDT is updated the first time traffic from a new device is detected
  • settings for number of devices attached to the port via ip device tracking max N
  • maximum number of probe times is 255

The Cisco docs on IPDT seem very scarce, so I figured I'd ask here:

  • Is there any way to force a refresh of this data?
  • Is there a way to reset the probe count once it's hit the max specified?
  • (is there even a way to see how many times ip device track info was probed for?)

The reason I'm interested in a way to force a refresh is two-fold. For one when a device is unplugged, I would expect it to disappear, but it doesn't. Also, for a switch where I've just enabled IPDT, not all devices plugged in appear immediately (though given enough time they do show up).

For reference, this is what I did to enable IPDT:

configure terminal       
ip device tracking              
int range Gi1/0/1-47
ip device tracking max 1  
ip device tracking probe count 255
ip device tracking probe interval 30
end
wr
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I don't think you are going to find exactly like what you want. The document to which you refer is the documentation; there's not a lot to this feature.

Refreshes happen automatically under the two circumstances detailed in the document, and there is nothing in place to force a refresh:

The ARP probe is sent under two circumstances:

  • The link associated with a current entry in the IPDT database moves from a DOWN to an UP state, and the ARP entry has been populated.
  • A link already in the UP state that is associated with an entry in the IPDT database has an expired probe interval.

You could shutdown/no shutdown a port to force a refresh, but that seems rather extreme.

Rather than changing the probe count, you could shorten the interval. Sending 255 probes every 30 seconds seems like a lot; it is nearly 10 per second.

You could get a close calculation for the number of time a port was probed by showing how long the port was up, divide that by the probe interval, and multiply that by the number of probes configured per interval.

There are also other features such as DHCP snooping which will build a database of MAC addresses and the DHCP assigned IP addresses.

If what you have doesn't suffice, you can always request added feature from Cisco, although your requested features may or may not make it into a future release. Cisco may also share a roadmap of planned enhancements to you.

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  • Thank you Ron. Is there an easier way to get just the connected MAC addresses per port, and be able to control a refresh on them? Dec 29 '15 at 20:19
  • The mac address table will have the MAC addresses per port, but it gets populated as traffic comes into the port. You can clear the table, but that causes excessive flooding as the switch relearn the MAC addresses.
    – Ron Maupin
    Dec 29 '15 at 20:22
  • So specifically I'd have to open a connection to that device to get traffic? Or is the DHCP traffic sufficient to have the mac address table updated? What's the best way to view the table? Dec 29 '15 at 20:28
  • The dashes depend on the IOS version, but, as I recall, show mac-address-table. The table automatically build as any traffic flows through a port;that'she how bridges work.
    – Ron Maupin
    Dec 29 '15 at 20:30

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