I am trying something very similar to Aux port for backup 5GHz link and for me, it creates a network loop in the remote V3000.
This is a v3000 connected to a v5000 with 5 other clients on the v5000. I attached a ePMP Force 180 to one of the V3000s that we lose in snowstorms (using a 48v to 24v converter). At the v5000 end, I put up another ePMP Force 180 as the AP.
We have Mikrotik routers on each end. The plan, since OpenR does not work in multi-point, was to create a new VLAN, put that on the ePMP link and use OSPF in the router to failover.
As soon as we bring up the 5GHz link, we lose IP connectivity to the far end router. It looks like a network loop is created but that loop does not leave the v3000.
On the v5000, it is connected via fiber to a 10G switch. Only tagged VLANs for those clients are on the switch port. The Force 180 AP is plugged into a different switch and only has a single VLAN tagged to it (different from those to the v5000). Nothing untagged.
On the V3000 client end, we have AUX port enabled and set to “Q” mode where we discard untagged packets and only allow VLAN 3006 - the backup 5 GHz path.
It is not possible to have a layer 2 loop in this scenario.
As soon as we bring up the 5GHz radio (or activate the Ethernet port on the AP side), we start to lose pings to the router at the far end. Not 100% of pings but a random sampling like you have in a loop situation. Customer traffic across the Terragraph link is disrupted. We have not even turned on the OSPF interface yet so there is no traffic trying to get across the 5GHz link.
We can stop the loop by either disabling the AUX port on the v3000 or admin down the Ethernet port on the AP side switch (but keeping the radio powered).
Long story to explain using the V3000 aux port for a separate backup link does not seem to work. Maybe OpenR is causing this?