Lets play IP 'Whack a Mole'

Had such a weird problem the other day after the installation of a voice switch.

The voice switch was manually configured  with an ip address (x.x.x.2) and an old Cisco switch (model unknown) decides to grab the same ip from our dhcp server.

Here's the odd part,  I configured the DHCP scope to start at x.x.x.11.

Since I was working remotely, I disabled the upstream switch port that the cisco switch was connected to until the onsite guys could investigate.

The onsite tech told me that the cisco switch was in an area that wasn't accessible, I suggested he hang tight and I will reenable the upstream switch port connected to the Cisco switch.

I enabled the port and we waited for about 15 minutes to see if the issue comes back. I could see the devices on the cisco switch had ip addresses and data was definitely flowing. Oddly enough the switch had not requested an ip address from the DHCP server with I confirmed via the switch mac table, router mac table and DHCP server.

I told the tech "lets leave it alone for the weekend'. Monday morning I checked and the Cisco switch is still online, I can see its mac address, but no ip address.

The tech decided to 'take it out'  when he got access since it was a super old 10/100 switch, so unfortunately I could no longer do any more testing, but still a good exercise on identifying, locating and isolating a duplicate ip address scenario.

 

---