Ubiquiti UniFi USG mDNS High CPU

At one educational client site we’re running a network with a USG Pro as the gateway, then VLANs and a primary LAN.

The issue we were having was, mDNS enabled through the “Services” interface on the UniFi Dashboard to make Apple TVs, printers, etc from the LAN accessible on the vLANs, was causing the USG Pro CPU to be 90%+

Upon investigating via SSH using “top” we found that “avahi-daemon” was the culprit, this is the mDNS reflector.

To fix this, we disabled mDNS through the Dashboard, then via ssh:

First we need to figure out the interfaces that we want to include in the repeater…

sudo ifconfig

This gives me eth0, eth0.15, and eth0.16 as my LAN, Staff, and Student networks.

Then ran the following to setup the mDNS repeater:

configure
set service mdns repeater interface eth0
set service mdns repeater interface eth0.15
set service mdns repeater interface eth0.16
commit ; exit

This worked, dropping the CPU down to 0% and functionality all working on the network, so to have these settings stick, we edited the config.gateway.json file on the controller and add a new section to the “services” portion.