Wi-Fi Troubleshooting

A Pointless Odyssey

For several months, my Wi-Fi has been incredibly slow. Over WiFi, I get speed test results equivalent to a connection from 15 years ago. Even YouTube has problems. We're talking about 5-10Mbit/s over Wi-Fi.

Measured at the RJ45 port of the Unify U7 In Wall with VLAN10 activated, I have a nice GBit/s:

Connecting to host 10.87.20.245, port 5201
[  5] local 10.87.10.59 port 46397 connected to 10.87.20.245 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.01   sec   111 MBytes   923 Mbits/sec
[  5]   1.01-2.00   sec   112 MBytes   942 Mbits/sec
[  5]   2.00-3.00   sec   112 MBytes   943 Mbits/sec
[  5]   3.00-4.01   sec   112 MBytes   936 Mbits/sec
[  5]   4.01-5.01   sec   110 MBytes   927 Mbits/sec
[  5]   5.01-6.01   sec   111 MBytes   925 Mbits/sec
[  5]   6.01-7.01   sec   112 MBytes   938 Mbits/sec
[  5]   7.01-8.00   sec   109 MBytes   926 Mbits/sec
[  5]   8.00-9.01   sec   114 MBytes   947 Mbits/sec
[  5]   9.01-10.01  sec   113 MBytes   943 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-10.01  sec  1.09 GBytes   935 Mbits/sec                  sender
[  5]   0.00-10.04  sec  1.09 GBytes   932 Mbits/sec                  receiver

Even when I remove the VLAN tag on the laptop and set the port as an access port for VLAN10 in the Unifi Manager, I get the same values. It seems like switching, routing, and tagging work properly. So it must be the WiFi settings, right?

After that, I tried resetting the AP and configuring it as a standalone AP, with only my notebook with a fixed IP and iperf3 at the uplink. But even there, only 4-7MBit/s.

Therefore, I found the following:

It's probably not the routing/switching, since I have Gbit throughput at the AP connection with the same devices
It's not the VLAN, all SSIDs, whether tagged or not, were equally fast
It's not the WiFi settings, as the same values were achieved with factory settings.

So there must be an interfering signal. The new PV system? But wait, I had the same phenomenon in the basement.

Just before giving up, I quickly rebooted my smartphone... Boom, 600MBit!!!

I now have two theories, but hardly have the opportunity to test them:

The WiFi stack in Android had some kind of problem
The network has a problem due to a faulty MAC table, and since Android varies the MAC (according to my settings), the problem has now been temporarily resolved.

Well, it's working now. But the path to get there was rather unsatisfying.