DHCP Snooping and Duplicate Address Messages From Clients

[Patrick McHenry]

Hi,

I've configured DHCP snooping on all of our User switches (3750X, 3850s). It works well , but there have been a couple fluky behaviors. One issue, and I can't be sure it is caused by the snooping, is a duplicate address error on laptops. but I've read a couple of docs regarding the issue and it seems to be in line with it.

Message and attachments I've received from users...

"The IP conflict shows in the event logs as conflicting with 0.0.0.0 and lists a mac address, but don't know what that mac belongs to and is different depending on date and VLAN.

Seems to only happen on laptops. The ones affected (as far as I know) are connected to both the wired & wifi, with the binding order set to used wired."

I've read through this doc and configured "ip device tracking probe delay 10" as suggested, but still seeing the issue.

The document also suggests using the command "ip device tracking probe interval <seconds>", but doesn't offer any suggested interval setting

Any further suggestions?

Thank you

Troubleshoot "Duplicate IP Address 0.0.0.0" Error Messages

[Mark Malone]

Hi

Get the mac address an trace it at layer 2 through the network ,. chances are someone has set a static ip on there devices which is causing the conflict , you should see these conflicts on switch logs as well

much easier to trace the mac through each switch to the port responsible then check the device connected see what its set for

example

trace this mac comes from port-channel 2 so dod sh cdp neighe see whats connected to po2 , then access that device and run same show mac again until you get to the end device the check its tcp/ip settings

5KCOREA# sh mac address-table address XXXX.983a.edf7
Legend:
        * - primary entry, G - Gateway MAC, (R) - Routed MAC, O - Overlay MAC
        age - seconds since last seen,+ - primary entry using vPC Peer-Link
   VLAN     MAC Address      Type      age     Secure NTFY   Ports/SWID.SSID.LID
---------+-----------------+--------+---------+------+----+------------------
* 74       XXXX.983a.edf7    dynamic   300        F    F  Po2