Got a weird issue on my CCR2004 (v7.15.1). The WiFi I use is UniFi. It seems that when a mobile device (Android or Apple) joins my Guest WiFi, it takes up 5 or 6 DHCP leases with MAC address 00:00:00:00:00:00 and then eventually gets an IP address. I only noticed it today because I was unable to con…

Proxy-ARP appears to have been the culprit, thank you! Out of interest, why would that have been the case? Just an increased amount of ARP traffic?

Do you have some special settings for your DHCP lease time (like unusually long or short)? With WiFi, sending broadcast and multicast packets is a very "expensive" operation, because those must be sent at the lowest common data rate (for example 6 Mbps or even only 1 Mbps), which means it takes sig…

Thanks a lot! Really helpful and detailed response.

Interesting stuff here. I really does seem that Ubiquiti proxy-arp is the root cause here, but I wonder about the mechanism. Looking around one of my access points, I cant find any setting for the arp cache timeouts in the GUI, and if you go to the cli all the arp settings are in line with Linux de…

Greetings. Same issue here. L009 with a Cisco 150ax AP for wifi. DHCP leases are not being recycled. Seems they are held until the device returns to give it the same IP. In the Cisco WAP, there isn’t a proxy-arp setting to check. In the router, I tried to set the bridge to “reply-only” for ARP in t…

Before switching the ARP mode on the bridge or VLAN interfaces to reply-only you have to make sure that the DHCP servers all have Add ARP For Leases turned on, so that they can populate the RouterOS ARP table with the content from the leases. For all devices that don't use DHCP but have manual addre…

Thank you for the reply. You were clear in your post, I wasn’t clear in my post. Apologies for that. I assign static addresses via the DHCP server. There are about 13 devices statically assigned via DHCP, the rest of the /24 block are acquired dynamically. Add arp for leases has been turned on sinc…

[image] MTNick: Not sure why these aren’t displayed in the export above Mikrotik exports normally only settings that are different from default, try with verbose parameter.

Greetings. Thank you. I have exported the config with verbose. Should I start a new thread since it’s a different WAP? Cisco vs Unifi. Or just post it here?

I don't see any reason to not continue here, the issue is the same, even if on a different device.

Mikrotik/Unifi WiFi DHCP Exhaustion?

RouterOS General

jaclaz October 16, 2025, 12:32pm 18

Is your Arp table "stale"?
Maybe you can try running a script to clean it, see (it seems to me a similar case to yours):