Wi-Fi is slow, the line is not

You have a fast connection, you measure it on a cable and it is right. The same test on a phone in the living room gives you a tenth of it. Nothing disconnects, it is simply slow, and often it is fine in one room and not in the next.

What it is not: if the cable is slow too, this is your uplink or your router, not your Wi-Fi. If one app is slow and the rest is not, it is that service. And if it is only slow in the evening, skip this and go to Everything is slow at peak hours.

The quick checks, in order

1. Measure on a cable first. Put a laptop on a LAN port and test. If that also gives you half your line, this is not a Wi-Fi chapter.
2. Look at what the client actually negotiates. /interface wifi registration-table print, or /interface wireless registration-table print on the old package. It shows the signal and the tx rate per client. A good answer on 5 GHz at 80 MHz is a tx rate in the hundreds of Mbit/s. A tx rate of 6, 12 or 24 Mbit/s means the client has fallen back to the slowest rates.
3. Is the client on the band you wanted? The registration table names the interface. If everything sits on the 2.4 GHz radio while 5 GHz is empty, that is the whole problem.
4. How much room is there on the channel? /interface wifi scan wifi1 duration=5. A channel shared with five neighbours is also shared in time.
5. Does the traffic go through the radio you think? Run /interface monitor-traffic interface=wifi1 during the test. That tells you straight away whether the radio is the bottleneck or something behind it.
6. Is the router not the brake? /system resource print, and if in doubt /tool profile duration=5. A lot of time in "networking" or "firewall" means the radio is not your problem.

The usual causes, most common first

The client is on 2.4 GHz

2.4 GHz is narrow, busy and slow. A phone that lands there stays there, even with a perfectly good 5 GHz signal two metres away. Band steering pushes new clients to 5 GHz. If one device stays stubborn, give 2.4 GHz its own SSID and move that device by hand.

Too far away, so a lower modulation

Wi-Fi does not become unreliable with a weaker signal, it becomes slower: the radio picks a more robust, slower modulation. That is what you are seeing when the tx rate is low while the connection is perfectly stable. More power on the router barely helps, because the client has to answer. An access point closer by does help.

A narrow channel, or a crowded one

20 MHz on 5 GHz gives roughly a quarter of what 80 MHz gives. The other way round: 80 MHz in a crowded building can give less than 40 MHz, because you spend more time waiting. There is no good default here, there is only measuring.

Old clients drag the rest down

A single 802.11b or 802.11g device on 2.4 GHz holds the air longer per packet, and that time comes off everyone else's. Put old and IoT equipment on its own 2.4 GHz SSID and leave 5 GHz alone.

The access point's own uplink

An access point on a 100 Mbit port, or behind a repeater, can never deliver more than that uplink. A repeater at least halves throughput, and with one radio doing uplink and broadcast at the same time about a quarter is left.

What the configurator does about it

• Band steering is on by default on devices with the new wifi package and more than one radio. It is the setting that gains the most here.
• Channel width 5 GHz defaults to 20/40/80 MHz and can be set narrower or wider. Channel width 2.4 GHz defaults to 20 MHz.
• Pick the repeater role in the Wi-Fi section and the tool warns that a repeater at least halves throughput and that a network cable to that device is always faster. On a single-radio device it adds that you should expect roughly a quarter of the router's speed.
• Draw the cabling on the network board with an internet speed on it and the check reports a port slower than the subscription, naming a better port. That is about the uplink rather than the radio, but it arrives as the same complaint.
• In a site, the check compares the SSIDs of every access point. If they differ you do not have one network with coverage, you have several networks.

What the tool does not do: pick a channel for you, enforce minimum data rates, or keep old clients out. Those controls are not in the schema, so they are not in this chapter either.

The honest limits

Wi-Fi is shared time in shared air. What the neighbours transmit counts against you even though it is not your network, and on 2.4 GHz so do microwaves and wireless cameras. A client picks its own band and its own rate, and some phones and laptops pick badly. And if your uplink is full, Wi-Fi gets slower while nothing is wrong with the Wi-Fi at all: check that with /interface monitor-traffic interface=ether1 on the WAN port.

Read on: Channels and width, Wi-Fi settings and Checks about speed.