How can I find a Rejected ARP Mac Address/Port?

  • 0
  • 1
  • Question
  • Updated 9 months ago
  • Answered
So if I type the "show iparp stats DATA001" command I can see some IP ARP stats for my network, at the core.  Down near the bottom I see Last Rejected ARP: along with the vlan and the port number.

This is good data for me as we are moving our edge over to extreme from nortel.  We are also switching up our vlan structure and require other departments to come in the night before and change their static IP's to match our new vlans.  The following morning, today, I decided to see what was not moved.

The "Last Rejected ARP"  cycles through a list of IPs that are rejected because most of them are still statically assigned to the old vlan.   However the problem is it only tells me the port # for the IDF it is connected to.    So it will say port 21, which might be IDF10 (edge)... thats a great starting place. 

However once I get to IDF10 i would like to be able to find the actual port the rejected ARP is coming from.  Being that the Last Rejected ARP only shows me an invalid IP, a Vlan, and a port off the core, how do I get closer to identifying the actual switchport that has the troublesome device?  If i could find a MAC address I could just do a show fdb and there it would be.

Thanks
Photo of Jared Sabin

Jared Sabin

  • 190 Points 100 badge 2x thumb

Posted 11 months ago

  • 0
  • 1
Photo of Patrick Voss

Patrick Voss, Alum

  • 11,714 Points 10k badge 2x thumb
Hello Jared,

I believe the only way to achieve this would be to temporarily put an IP on the edge switch VLAN. This will allow you to look at the same iparp stats you are looking at on the core and allow you to find the offending ports.
Photo of Jared Sabin

Jared Sabin

  • 190 Points 100 badge 2x thumb
That seemed to work, thanks!

Another question, is there a way to see a log of rejected ARP requests?  Trying to catch them while they cycle really fast can be hard.