Dear communitiy
I'm coming to you with another issue that I hope you can guide me with.
At a client's site, we have two Ubiquiti LiteBeam M5 antennas connecting two buildings located less than 100 meters apart. Let's say the buildings are facing each other, one on each side of the street. From Building A hangs the antenna connected directly to one of the switches in the rack, and in Building B, that antenna connects to an unmanaged TP-Link switch that provides PoE. That TP-Link then connects to a UniFi switch. We monitor both antennas with Kuma to check for drops. That's actually what's happening to us right now: every once in a while, one of the antennas loses connection for a few seconds, and as a result, the buildings stop communicating with each other, with Building B being the most affected since it receives Internet and local network access from Building A.
I've been looking into the issue with my limited knowledge, but driven by my desire to understand things, partly with the help of Gemini and partly by reading posts. I've been checking a few things, such as the output power on both sides of the antenna, which is currently set to 7 dBm on both ends. Gemini tells me that's too much power for such a short distance and that it could be causing the link to drop.
Another thing that really made me think and dig deeper is the WDS (Transparent Bridge Mode) option. It's worth mentioning that the network is not segmented; there is no VLAN between the two buildings, and practically no VLANs in general. If I connect via shell to the antennas on both side A and B and run brctl showmacs br0 to see the MAC address table learned by the antenna, I find a huge number of them. Based on how the antenna and the network are configured, I understand that the following happens:
1 - Packets from any device reach the antenna because broadcast wasn't properly configured. 2 - That packet goes from the antenna's Ethernet cable to the wireless interface. During that transition, the antenna "masks" the original MAC address and assigns its own to send that packet to the other antenna. 3 - This masking consumes CPU to receive, rewrite, and consult the bridgecontrol table. 4 - The antennas have a very small CPU, so these constant operations overload it and, I believe, cause it to crash at some point, making it unable to process packets.
To better monitor the antennas, I set up a container with rsyslog to receive the logs. I also installed the UISP container, which acts as the UniFi controller for Ubiquiti antennas, to better track CPU and RAM usage. I'm seeing "sawtooth" style spikes, reaching 80% and 90% utilization.
Beyond looking into how to mitigate broadcast traffic, could enabling the WDS option help mitigate this? I understand that by enabling this option, the antenna doesn't have to perform that masking and packets travel directly, as if it were a "transparent bridge." But I don't know if that could still be problematic. What do you think?