unifi-wifi

UniFi Wi-Fi

Most "slow Wi-Fi" is not slow Wi-Fi. It is a WAN problem, a backhaul problem, a client problem, or a bandwidth cap somebody set two years ago. The diagnostic ladder below exists to find that out cheaply, in that order, before touching radios. Radio changes are the most disruptive and the most often wrong.

The diagnostic ladder

Run it top to bottom. Each rung eliminates a layer, and the failure that motivated this skill was only visible at the last rung.

1. Rule out the WAN. Trigger a gateway-side speedtest, which measures the gateway to the internet with no Wi-Fi involved:

udm raw POST /proxy/network/api/s/default/cmd/devmgr '{"cmd":"speedtest"}'
# wait, then read the RESULT from stat/device, not stat/health
udm devices --json | python3 -c '
import json,sys
for d in json.load(sys.stdin):
    s = d.get("speedtest-status")
    if s: print(d.get("name"), s.get("xput_download"), s.get("xput_upload"),
                "status_summary=", s.get("status_summary"))'

The result lands on the gateway's device object, under the hyphenated key speedtest-status (not speedtest_status), with throughput in the nested xput_download and xput_upload fields. status_summary tells you whether the run finished; a fresh gateway that has never run one reports zeros. stat/health is a different number entirely and will send you in circles.

2. Check the AP's uplink. An AP on a 100 Mbps link, or meshed rather than wired, caps every client behind it:

udm devices --json | python3 -c '
import json,sys
for d in json.load(sys.stdin):
    up = d.get("uplink") or {}
    print(d.get("name"), d.get("type"), up.get("speed"), up.get("type"))'

3. Check the client's own view. Signal, negotiated rate, satisfaction:

udm clients --json | python3 -c '
import json,sys
for c in json.load(sys.stdin):
    print(c.get("hostname"), c.get("signal"), c.get("tx_rate"), c.get("satisfaction"))'

This rung is where the interesting case appears. A client at -57 dBm with an 866 Mbps PHY rate has an excellent link. If it measures 32 Mbps, the radio is fine and something is contending. Signal is not throughput, and confusing the two is why people replace working access points.