topic Re: Multiple DHCP servers Detected in Wireless

Multiple DHCP servers Detected

zfrangi — Fri, 03 Dec 2021 21:16:44 GMT

I keep getting alerts in my event logs about Multiple DHCP servers being detected. Im running all Meraki MR34's in our environment and our dhcp servers reside on our windows servers. Is there any way I can find out where this is coming from?

Re: Multiple DHCP servers Detected

zfrangi — Fri, 03 Dec 2021 21:18:55 GMT

Forgot to mention in the logs it shows a mac address which when I look it up it come back to cisco. Im assuming its our switch however to my knowledge they arent doing dhcp.

Re: Multiple DHCP servers Detected

Brandon Svec — Fri, 03 Dec 2021 21:38:17 GMT

The MAC addresses are your clue. You need to check what devices they match in your network.

Re: Multiple DHCP servers Detected

BlakeRichardson — Mon, 06 Dec 2021 01:52:15 GMT

If you go to Switches > Monitor > DHCP & ARP it should give you a list of active DHCP servers on your network.

If you don't have Meraki switches I would run a packet capture and see if you can work out what devices respond to a DHCP request.

Re: Multiple DHCP servers Detected

zfrangi — Mon, 06 Dec 2021 14:02:27 GMT

I do not have meraki switches...I have cisco switches. How can I go about tracking down this mac address?

Re: Multiple DHCP servers Detected

zfrangi — Mon, 06 Dec 2021 14:06:29 GMT

I have a dumb question on this event log entries....I see the following.....

vap: 0, original_server_ip: 172.22.81.29, original_server_mac: 30:E4:DB:13:C7:46

server_ip	172.22.66.2
server_mac	30:E4:DB:13:C7:46

So which one is the dhcp server? I guess my question is how do I decipher whats going on here?

Re: Multiple DHCP servers Detected

zfrangi — Mon, 06 Dec 2021 15:28:46 GMT

After further investigation i was able to uncover that 66.2 is a vlan interface on the switch. There is an ip helper entry that points to 81.29 which is a windows dhcp server. So is this entry normal behavior?

Im seeing similar messages on all of our networks.

Re: Multiple DHCP servers Detected

JohnMaida05753 — Wed, 08 Dec 2021 19:45:01 GMT

I had this issue with multiple IP helpers configured on an SVI. Especially if you use ISE for profiling.I believe Meraki support can make a back end change for this.

Re: Multiple DHCP servers Detected

MarkB — Thu, 30 Jun 2022 12:47:35 GMT

Hi,

Did you get an answer to this from Meraki ? Is it normal behaviour?

Thanks

Mark