Xiaomi Router 4A is available in 100M and Gigabit versions, and the 300M broadband only runs 90M

Last month, my third uncle sent me a voice message on WeChat, and there was the sound of TV in the background.: 「Nephew, is the 300M installed in my home a fake broadband? The mobile phone measured 88 MB. 」My first reaction was that the optical modem was plugged into the wrong port or the network cable had four cores. I took my laptop over the weekend and plugged the network cable directly into the router's LAN port. The moment the negotiated rate popped up, I didn't need to check again - 100Mbps. Turn over the router and look at the bottom label, Xiaomi Router 4A, followed by a line of small words: 100M。

Before going, I asked him to take two steps on the phone.: Check the optical power in the backstage of the optical modem, it is negative 21, the optical path is fine. ； The mobile phone stood in front of the router and was connected to the 5G band to measure 88 MB. The computer network cable was directly plugged into the LAN port and the 5G frequency band was measured to be 92 MB. Wireless and wired are all stuck at around 90 Mbit/s. This digital characteristic is too typical - the bottleneck is neither in the air nor in the wall, but in a place where all traffic cannot be bypassed. I went to the scene and flipped the labels, closing the loop.

Make it clear first: 4A is one name, two machines

This matter has to start from 2018. At that time, the competition in the hundred-yuan router market was fierce. Xiaomi made two versions of the 4A and sold them at the same time. They were both called "Xiaomi Router 4A", one was a 100M version and the other was a Gigabit version. The price difference was dozens of yuan. The store talks about "4A". Which one you get depends on the purchase and luck. Uncle San's was given to me by the computer store in town when it came with broadband, so the one given was naturally the cheaper one.

I will make a table of the two versions of accounts, and you can see the difference at a glance.:

Pay attention to the wireless line. Both versions have the same dual-band AC1200. This is where it gets deceptive: Just looking at the WiFi name, signal grid number, and background interface, there is almost no difference between the two machines. Even the background looks the same. The difference is all in the network port you can't see and the chip in your belly.

The difference is more than one network port: The chip is one generation different

The 100M version of MT7628DA is the predecessor solution of MT7621A, with a single core of 580MHz and a dual core of 880MHz, and only half the memory. When running under full load, the margin for NAT forwarding is not an order of magnitude at all. The Gigabit version also has independent PA and LNA, and the attenuation performance of signals in the same room and through walls is also much better. You may not be able to feel it when you swipe your phone every day, but if there are too many devices at home and some people are watching live broadcasts and downloading things, the 100M version will be stuck first.

For the Tossing Party, this gap is even more fatal: The Breed and firmware of the two machines are completely incompatible. The solution ecology of MT7621A is very mature. If you want to copy the tutorial for the 100M version, it will restart infinitely if you continue to refresh it. Therefore, for people who use second-hand training, admitting the wrong version is equivalent to spending a whole night's work in vain.

Uncle San also added some useful information.: This machine was hot to the touch in the summer, and it would break every now and then at night. When it did, he would unplug it and plug it back in again. The single-core 580MHz usually has a high load, and if the heat dissipation becomes blurry, disconnections will follow. This is not an exception. For small machines with full configurations such as the 100M version, it is normal for Tianyi thermal stability to be released first.

Three tips for identifying editions: Don’t trust the seller’s words, trust the label and negotiation speed

The first step is to scroll through the bottom tab. The label of the 100M version has "100M" printed next to the model number, but the Gigabit version does not have this line. This is how Uncle San recognized this station. It only took ten seconds. If you look at the packaging box of a new, unopened model, the words "Gigabit version" are clearly printed on the box. Those without these three words are the 100M version.

The second trick is to plug the network cable into the computer and check the negotiated speed. This is the most accurate trick. Plug the network cable into the LAN port, wait two seconds, Windows will check the network connection status, and Mac will check the link speed in the network settings. It is negotiated that 1000Mbps is the Gigabit version, and 100Mbps is the 100M version. The whole process takes thirty seconds, which is more civilized than disassembling a phone and more reliable than asking the seller - anyone can type the words "Gigabit version" on Xianyu.

The third trick is to ask the flash party about the firmware version. The Gigabit version itself is divided into two generations of hardware: V1 and V2. The firmware version of V1 starts with 2.28.x. If there are ready-made open source solutions, just follow them. ； You have to compile the firmware of V2 yourself, novices should not touch it. Before accepting the purchase, ask the seller to take a screenshot of the background system status. The version number will be clear at a glance, saving you the trouble of scratching your head.

This is how 90 trillion came about: The 100M port is the main gateway for the whole family

The third uncle is not convinced.: 「The 5G WiFi connected to my mobile phone has a full signal, but it’s only 90 MHz? 」I gave him signs: WiFi is from home to the router. It is really fast. The 5G band can reach 867 MB through negotiation. But when going out from the router to the operator, the whole family's traffic has to squeeze through the 100Mbps gate at the WAN port. No matter how busy it is inside, there is only a narrow path out.

100Mbps is converted into a theoretical maximum download speed of 12.5MB/s. After deducting the protocol overhead, the actual measured stability is between 90 and 95 MB, which is the normal level of this gate. The third uncle's house is 88MB, no more and no less, just stuck on the ceiling. This digital feature is exactly the same problem as the optical modem plugged into the wrong 100M port. I am The article about optical modem Gigabit Port and 100 Mbit Port I wrote a comparison table here. If your home network speed is stuck at around 90 Mbit/s for a long time, you should first suspect the 100 Mbit/s link, and don’t blame the operator first.

As for how to convert megabytes to MB, and how many megabytes of broadband is enough to install at home, I used to How many megabits does broadband install? I did some detailed calculations in that article, one sentence version: Divide the number of megabytes by 8 to get the download speed you see.

What use will these two have in 2026?

Let’s talk about the conclusion first: When used as the main router, both routers are unqualified. As mentioned before about the 100M version, although the Gigabit version has no problem with the interface, it is fine to run a basic NAT with dual-core 880MHz and a few hundred Mbps broadband. Once there are 30 or 40 devices in the home and some additional functions are turned on, it will suffer. The third uncle finally listened to me and bought an AX3000T for 129, plugged it in and measured 294 MB, and apologized to the operator on the spot.

But it’s not a mistake to just throw them away. Each has its own destiny. The most suitable position for the 100M version is 2.4G IoT private network ： Sweepers, cameras, thermometers and hygrometers, these devices that only recognize 2.4G and have small traffic, are maintained on a separate network and do not compete with the mobile phones and computers on the main network. This is how my old AC2100 was modified. Change AP to feed 14 smart devices I have written the process. Just follow the same process for the 100M version. Anyway, the traffic of each of these devices is only a few hundred KB. Why should old equipment have a separate network? The account of air interface time occupied by old equipment You’ll understand if you look at it.

The Gigabit version is worth picking up and practicing. MT7621 plus 128MB of memory is a classic foundation in the flashing industry. The second-hand price is between 40 and 50 to 70 and 80 yuan. It is more than enough to flash OpenWrt as a bypass router and run lightweight plug-ins. If you want to get started with flashing your phone, read this first How to unlock SSH , take another photo The process of flashing OpenWrt on AX3000T take the idea ； Some people use the older MT7620 platform as a bypass route. My R3 is Padavan He is still serving at my mother's house.

By the way, let me mention 4C. It is the re-sword version of the 4A 100M version: The same MT7628DA is equipped with 64MB of memory, which cuts off the entire 5G frequency band, leaving only 2.4G single frequency 300M, and the network port is still 100M. Today, there are still stores selling it as "Xiaomi's new model" for 40 to 50 yuan. It is really useless as a main router. Like the 100M version of 4A, it is only suitable for carrying Internet of Things devices. I really want to buy a new one for my parents’ house. It’s only 100 yuan. I have used AX3000T for two years The basics and version pitfalls have been written down, so just avoid them.

Give an order at the end

If you have 4A in hand, first look at the label to identify the version, and then check the broadband megabytes at home.: Below 200 Mbit/s and there are not many devices, the 100 Mbit/s version is just fine. ； The broadband is up to 300 Mbit/s, so don’t hesitate to change it. When buying second-hand products, I was asked three questions in a row - 100M or Gigabit, V1 or V2, and what is the firmware version number. If the seller couldn't answer the answer, he asked him to take a screenshot of the background. If you buy a new phone, look for the "Gigabit version" on the package, or simply buy the AX and BE series from the past two years. Don't gamble on twins with the same name. The third uncle's 100M version is now running six smart devices at my cousin's house. He retired and returned to work, and he is doing a great job.