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.

4. Rule out a bandwidth cap. Somebody, possibly you, may have set one:

udm raw GET /proxy/network/api/s/default/rest/usergroup
udm wlans --json    # check per-SSID rate limits

5. Compare every AP's channel, width, and channel utilization. The last rung, and the one that finds co-channel contention:

udm devices --json | python3 -c '
import json,sys
for d in json.load(sys.stdin):
    for r in d.get("radio_table_stats") or []:
        print(d.get("name"), r.get("radio"), "ch", r.get("channel"),
              "bw", r.get("bw"), "cu_total", r.get("cu_total"),
              "sat", r.get("satisfaction"))'

Field names matter here and are not the obvious ones. Channel width is bw, not channel_width. The names are per object, not global: on a client record the same value really is channel_width. Check the object you are reading rather than carrying a field name across from another endpoint. cu_total is channel utilization, the percentage of airtime in use, and it is the closest thing to a direct measurement of the problem this skill is about. cu_self_tx and cu_self_rx break out how much of that is this AP's own traffic: high cu_total with low cu_self_* means somebody else is using your airtime, which is either a neighbor or, more often, your own AP two rooms away on the same channel.

satisfaction reports -1 when a radio has no clients on it. That is "no data", not "terrible".

Read radio_table_stats, the operational state, not radio_table, the config. They disagree more often than you would like.

The 80 MHz trap

The failure that motivated this skill, because it is a change that looks free.

Setting every 5 GHz radio to 80 MHz doubles the theoretical per-client rate, so it reads like a pure upgrade. It is not, because width is bought with channels. In the US regulatory domain, 80 MHz with DFS channels disabled leaves exactly two non-overlapping blocks:

• UNII-1: channels 36 / 40 / 44 / 48
• UNII-3: channels 149 / 153 / 157 / 161

Two blocks. If you have more than two 5 GHz APs with overlapping coverage, some of them are sharing an 80 MHz block and taking turns transmitting. Wi-Fi degrades gracefully in signal terms and catastrophically in contention terms: everything looks healthy right up until two clients are busy simultaneously.

The observed case: four APs, three of them in-wall units on adjacent walls, all piled into UNII-1 after a global switch to 80 MHz. Result was roughly 32 Mbps on a gigabit connection, with an 866 Mbps PHY link at -57 dBm and a confirmed 1276 Mbps gateway speedtest. Neither ISP, backhaul, nor signal was the cap.

Do not disable DFS channels when auditing a channel plan. It is the change that creates the pileup. DFS is the difference between two usable 80 MHz blocks and six.

Pick a block, not a channel

At 80 MHz a radio occupies its whole block, so two APs on different channels in the same block are fully co-channel with each other. This is the mistake to avoid when spreading APs out: moving an AP from 48 to 104 accomplishes nothing if another AP already sits on 100.

US 80 MHz blocks:

Map what you have to blocks before choosing a target, because the channel numbers hide the collision:

udm devices --json | python3 -c '
import json,sys
B=([36,40,44,48],[52,56,60,64],[100,104,108,112],[116,120,124,128],[132,136,140,144],[149,153,157,161])
blk=lambda c: next(("%d-%d"%(b[0],b[-1]) for b in B if c in b), "?")
for d in json.load(sys.stdin):
    for s in d.get("radio_table_stats") or []:
        if s.get("radio")=="na" and s.get("channel"):
            print(d.get("name"), "ch", s.get("channel"), "-> block", blk(s["channel"]))'

Prefer 52-64, 100-112, and 132-144 when you need free blocks. The 116-128 block overlaps terminal doppler weather radar (TDWR, 5600-5650 MHz) in the US, where a CAC can run ten minutes instead of one, and the channels are sometimes unavailable outright. An 80 MHz block anchored at 116 spans 116/120/124/128 = 5570-5650 MHz, so it swallows the whole TDWR sub-band: at 80 MHz you cannot sit near 116 without sitting in it.

If an AP keeps falling off a DFS channel, stop restarting it

An AP assigned a DFS channel can run there for a week or two, hit a radar detection (real or false), quietly move to a non-DFS channel, and keep reporting the assigned channel in its config the whole time. Nothing alarms, nothing logs it, and rest/device echoes back whatever you last wrote. One deployment sat like this for twelve days: config said 116, the radio was on 149, stacked on top of two APs already sharing the 149-161 block, at 33% and 30% channel utilization while every other AP sat at 1-2%. Every check had read the config.

Restarting puts it back and buys another week or two, which is treating the symptom. If a radio keeps getting pushed off the same block, the block is wrong for that site. Retire it and take an extra co-channel share instead. Moving that AP to a non-DFS block took it from 33% to 7% utilization and its neighbour from 21% to 12%. A share you chose beats a channel the AP cannot hold, so pair whichever APs are furthest apart physically: different floors beats different rooms.

Audit live-vs-config, not either one alone, on a schedule rather than only after a write. A radio that drifts once will drift again.

udm devices --json | python3 -c '
import json,sys
for d in json.load(sys.stdin):
    cfg={r["radio"]:r for r in d.get("radio_table") or []}
    for s in d.get("radio_table_stats") or []:
        c=cfg.get(s["radio"],{}).get("channel")
        if s.get("channel") and str(c)!=str(s["channel"]) and c!="auto":
            print("DRIFT", d.get("name"), s["radio"], "cfg", c, "live", s["channel"])'

The tradeoff is real and worth stating honestly: DFS channels require radar detection, cost a ~50-60 second silent scan when a radio moves onto one, and some older or cheap client devices will not associate on them at all. Weigh that against four APs sharing one block. In a dense deployment, 40 MHz on non-overlapping channels beats 80 MHz on shared ones, every time.

Changing a radio channel safely

Read and write are different endpoints. This one costs people an hour:

GET  /proxy/network/api/s/default/stat/device/<MAC>       # the object
PUT  /proxy/network/api/s/default/rest/device/<DEVICE_ID> # the write

GET rest/device returns an empty list on Network 10.4.57, with or without a device id appended, exactly like rest/firewallrule in unifi-firewall. It is not broken and your key is fine: reads live on stat/device. An agent that GETs rest/device, sees [], and concludes the controller has no devices is on the wrong endpoint.

The write body that works is the radio table alone, sent complete:

# GET the device, edit ONLY the target field inside radio_table,
# then PUT the WHOLE radio_table array back:
udm raw PUT /proxy/network/api/s/default/rest/device/<DEVICE_ID> \
  '{"radio_table": [ <every radio, every field, one value changed> ]}'

Verified on Network 10.4.57: this preserves the radio you did not touch. You do not need to send the entire device object back, and you should not, because stat/device hands you a pile of read-only operational fields along with the config.

Send the full radio_table array. A partial write drops the fields you omitted, including transmit power and width on the other radio.

channel may read auto in config while radio_table_stats shows a real number. Those are both correct: the AP is auto-selecting and has landed somewhere. Writing a concrete channel silently opts that radio out of automatic selection, which is usually what you want for a deliberate plan, but it is a second change riding along with the first. Know you are making it.

Moving onto a DFS channel triggers a CAC (channel availability check) and the radio goes silent for it. Two moves observed on Network 10.4.57 took roughly 45 and 105 seconds, so budget more than a minute and do not conclude the write failed at the 60-second mark. Clients drop and reconnect once. Do it when nobody is on a call.

The two directions are not equally hard. Moving off a DFS channel onto a non-DFS one is easy: one observed move settled about 75 seconds after a force-provision, no restart, clients reassociating on their own. Moving onto a DFS channel is where it sticks, and a force-provision can leave the radio on its old channel indefinitely; an AP restart (cmd/devmgr restart, ~2.5 minutes offline) is what finally lands it after CAC. If a non-DFS move needs a restart, something else is wrong. Go look rather than power-cycling.

Verify from radio_table_stats, never the PUT echo, and read state rather than just channel:

A radio still reporting the old channel with state: RUN has not moved yet. One in DFS_WAIT is moving and needs more time.

udm devices --json | python3 -c '
import json,sys
for d in json.load(sys.stdin):
    for s in d.get("radio_table_stats") or []:
        print(d.get("name"), s.get("radio"), s.get("channel"),
              s.get("state"), "clients", s.get("num_sta"))'

Roaming

Nothing here makes a client roam. The client decides, every time, using logic its vendor did not document and you cannot change. Every setting below either changes what the client sees or takes the current AP away from it. Read that again before spending an evening on thresholds: this is lobbying, not commanding.

A sticky client is usually not a roaming problem. It is a cell-size problem. An AP loud enough to be heard comfortably three rooms away gives a client that walks that far a perfectly good signal and no reason to move. Fix coverage overlap first. The persuasion knobs compensate for a cell plan, they do not replace one.

What the controller exposes, and where

Two different objects, which is the first thing that trips people up.

Per SSID, in rest/wlanconf:

Per radio, in each device's radio_table:

Every field name above was read off a live controller on Network 10.4.57. There is no 802.11k neighbor-report toggle in either object on this version. If a guide tells you to enable 11k in UniFi, confirm it is not describing a different controller generation.

Order of operations

Work down. Each step is cheaper to undo than the one after it.

1. Size the cells with transmit power. The most effective fix and the least clever one. In a dense deployment, turning power down improves roaming: a smaller cell means the client runs out of signal while a better AP is already well within range.

Set every AP covering the same area to the same mode. One AP left on auto among manual neighbors resizes its own cell on its own schedule while everything around it holds still, so the overlap you designed drifts without you touching anything.

udm devices --json | python3 -c '
import json,sys
for d in json.load(sys.stdin):
    for r in d.get("radio_table") or []:
        print(d.get("name"), r.get("radio"), r.get("tx_power_mode"),
              r.get("tx_power"), "range", r.get("min_txpower"), r.get("max_txpower"))'

Two things observed on real mixed hardware:

• min_txpower and max_txpower differ per radio and per model. Ranges of 6..22, 6..26, and 4..20 were seen across three AP models on one network. A single dBm value applied network-wide is not portable, and a value outside a radio's range is not a setting.
• tx_power does not track tx_power_mode. Radios reporting mode low were observed carrying tx_power values of both 6 and 20. When the mode is a named preset, read tx_power as a leftover, not as effective radiated power.

2. Raise the minimum data rate. minrate_na_enabled plus minrate_na_data_rate_kbps sets a floor. Slow frames from a distant client consume airtime far out of proportion to the data they carry, and a client that cannot meet the floor has to go find an AP where it can. Gentler than a disconnect, and it attacks the contention problem from earlier in this skill at the same time.

3. Enable 802.11r and 802.11v. fast_roaming_enabled shortens the reassociation handshake; bss_transition lets the AP nominate a neighbor. Neither forces anything, and 11v suggestions are routinely ignored. 802.11r has a long history of breaking older clients, so turn it on for one SSID and watch what stops connecting rather than flipping it everywhere at once.

4. Only then consider a minimum RSSI. Read the next section first.

The min RSSI trap

Minimum RSSI is not a handoff. It is a disconnect. The AP stops answering a client below the floor, and what happens next is entirely the client's choice. That includes immediately reassociating to the same AP, which is a disconnect loop wearing a roam costume.

Two thresholds exist and they are not the same knob: min_rssi is per radio in radio_table, roaming_assistant_na_rssi is per SSID in wlanconf. Both can be active simultaneously. Which one wins when they disagree is not established here, because settling it means writing to a live network and watching clients drop. Read both before changing either.

min_rssi and min_rssi_enabled are independent, so read the flag, not the number. A radio will happily report min_rssi: -79 with min_rssi_enabled: False, and that threshold is doing nothing. Observed on Network 10.4.57 with the flag True on every 5 GHz radio and False on every 2.4 GHz radio of the same APs. Auditing the values alone tells you a story that is half wrong.

Before changing a floor, find out who it will evict. A tighter number is only free if nobody is living in the gap:

udm clients --json | python3 -c '
import json,sys
for c in json.load(sys.stdin):
    s=c.get("signal") or 0
    if c.get("radio")=="na" and s and s <= -75: print(c.get("hostname"), s)'

Set it too aggressive and you have built a coverage hole out of software. A client evicted at -70 that sees nothing better than -72 has nowhere to go, and the symptom is not poor roaming, it is a device that will not stay on the network at all. Anything tighter than roughly -75 needs a specific reason.

Keep the floor consistent across APs covering the same space. Values drifting between -70 and -79 on one network is the pathological case: the AP with the tightest floor evicts clients that every neighbor around it is perfectly happy to serve.

Checking whether any of it worked

The controller will not tell you. Client records carry roam_count, and comparing it across a few days is a far better signal than reading it once:

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

Run it, walk the building, run it again. ap_mac changing is a roam. signal improving after it changed is a good roam. A roam_count that climbs while the device sits still is thrash, and usually means a threshold is too tight.

Check fixed_ap_enabled and fixed_ap_mac before diagnosing anything. A client pinned to a specific AP will not roam no matter what you tune, and the setting is easy to apply once and forget:

udm clients --json | python3 -c '
import json,sys
for c in json.load(sys.stdin):
    if c.get("fixed_ap_enabled"):
        print("PINNED", c.get("hostname"), c.get("fixed_ap_mac"))'

Applying the change

wlanconf and radio_table are both full-object PUTs, so the discipline from unifi-connect applies unchanged: GET the whole object, change one field, PUT the whole thing back, re-read to confirm. Roaming work is the easiest place in this API to lose a passphrase or an entire transmit-power plan to a partial write.

Whether a given roaming change needs a force-provision to take effect was not established here. If a setting reads back correctly but behaves as though it never applied, udm devices provision <MAC> is the next thing to try.

SSID hygiene

udm wlans --json | python3 -c '
import json,sys
for w in json.load(sys.stdin):
    print(w.get("name"), w.get("enabled"), w.get("security"), w.get("networkconf_id"))'

• Re-read enabled on every wlanconf touch. An SSID that was deliberately disabled can come back: a controller update, a config restore, or somebody in the UI. Deliberate disables do not always stay disabled, so make checking the state part of the routine rather than assuming your last change held.
• Never leave an open SSID on the trusted network. If a device genuinely cannot do WPA2, and some old handhelds and IoT gear cannot, rebuild that SSID on the guest or IoT network where an open join reaches nothing. An open SSID bridged to the trusted LAN is an unauthenticated port on your network with a radius of about 40 metres.
• Hidden SSIDs are not security. They are broadcast in probe requests by every client configured for them. They mainly make life harder for you.
• Confirm each SSID's networkconf_id maps to the network you think it does. This is how a device ends up on the trusted VLAN despite a careful segmentation plan: it joined the SSID that was still pointed at the old network.

The in-wall AP port trap

Filed here because it is AP hardware behavior, though it bites during wired segmentation.

AC-series in-wall APs do not enforce native-VLAN overrides on their pass-through data ports. Set a port override on the AP, and the controller accepts it and echoes native_networkconf_id back in port_table as though it applied. The operational forward value stays all, and untagged traffic from the device behind that port keeps bridging onto the AP's own network.

Verified with two force-provisions and a forward:'native' variant. The device behind the port stayed reachable on the old subnet throughout, which is the tell: the config says isolated, the network says otherwise.

Devices behind in-wall AP data ports cannot be VLAN-jailed. Not a configuration problem, so do not burn an afternoon on payload variants. Re-cable to a real switch port, or accept it and document the exception. Once you know this, it takes ten seconds to check whether a stubborn device is behind one.

A disabled radio may not be disabled

Same hardware family, same shape of lie, and this one has an ongoing cost.

Two In-Wall HD APs on Network 10.4.57, both with a 2.4 GHz radio configured off and parked on channel 11 at 20 MHz. What they were actually doing:

Every configured value ignored, and cu_self_tx of 5 to 6 percent means each one was spending real airtime beaconing to nobody, on the channel where a third AP was serving every 2.4 GHz device in the building.

num_sta: 0 does not mean a radio is idle. A radio with no clients still beacons, and at 40 MHz from channel 1 it covers most of the band. Judge a radio by state and cu_self_tx, never by client count.

Things that did not fix it, so you can skip them:

• Force-provision, twice. The stored config was not applied either time.
• "enabled": false on the radio entry. The PUT returns rc: ok and the controller silently strips the field: it does not survive a read-back and it is not part of the radio_table schema. A clean illustration of why rc: ok is not evidence, and why a round-trip read is.

An AC In-Wall on the same site, with the same tx_power_mode: disabled, sits at state: INIT with no channel and zero utilization, which is what genuinely off looks like. Whether that radio is disabled or simply failed to initialize is not distinguishable from the API, so treat it as a clue rather than a conclusion.

If you need a radio truly off on this hardware, do it in the UI and then diff. GET the device's radio_table, toggle the radio in the web interface, GET again, and compare. That tells you the field the controller actually writes. Do not invent one: the guess above looked entirely plausible and was silently discarded.