Is it difficult to flash OpenWrt on a Xiaomi router 4C? 30 yuan to buy a phone to practice without disassembling or breeding, only daring to use your main phone after training

last month, I did something I hesitated for over half a year: flashing OpenWrt on the AX3000T at home that had been used for two years. I didn't dare to buy because I was bold; before I started, I spent 30 yuan to buy a second-hand Xiaomi router 4C and used it to walk through the entire process from start to finish. A 30-yuan machine breaks down, and the pain lasts three minutes; If the main unit bought for 180 or 90 yuan breaks down, that's like squatting in front of the weak current box smoking half a pack of cigarettes. This article will clearly describe my entire process of practicing with 4C devices and the pitfalls I've made, offering the cheapest path for those who want to learn to flash but can't bring themselves to do it.

why spend 30 yuan on an old 2018 machine

first explain the motivation for buying the machine. I've always wanted to play OpenWrt—not because I need any features, but because I've tinkered with my home network so much that I always feel a barrier in my heart if I don't personally swipe the machine or glance at the LuCI interface. But every time I read the tutorial, the line "flashing is risky, be cautious about bricking" retracts the text. I've also flipped through posts about brick rescue, CR6609 the kind where flashing fails yellow light and slow flash, TTL wiring and disassembly wiring—those thresholds are still out of reach.

later realized a truth: the most expensive cost of learning to flash a machine isn't time, but the machine that might get damaged. Instead of gambling on your main machine, it's better to spend the money of a meal on a machine specifically designed for breaking down. On Xianyu, you can pick any Xiaomi 4C of its quality, 15 to 35 yuan each. I got one with a power supply for 30 yuan, and the seller even added a comment: 'Can you really sell this thing for money?'

choosing 4C is not something you pick casually. First, it's cheap—if you farm bricks, the tuition cap is 30 yuan. Second, it's an old machine, released in July 2018. The firmware from that era still had loopholes, unlike AX3000T new machines that tightly block official channels, you have to bypass the system. Third, it's so cheap that you can confidently click every step. This 'just make it anywhere' mindset is exactly what practice needs most.

4C first figure out its foundation: what it can and cannot do

Before

collecting the machine, you need to know what level it is—don't expect it to be misaligned. The foundation of 4C can be summed up in one sentence: entry-level phones in the WiFi 4 era. I'll make a table for the specific specifications, and when buying second-hand, just check accordingly.

see the problem: single-frequency, 100MB port, 64MB memory—any one of these three means it can't serve as the main router at home. when I wrote about the 4A 100Mbps and gigabit versions before I put 4C in the 'don't use it as the main router' category. If you use a 30-yuan machine to run gigabit broadband, plugging in the network cable is a loss the very second.

but practicing doesn't require performance. The flashing process has nothing to do with the machine's grade. The 580MHz single-core runs telnet and performs MTD writes. Every step you learn on 4C devices is copied exactly on any old Xiaomi model. This is the value of cheap machines: the process is universal, and the tuition is one-time.

the path of flashing the phone: no disassembly or breeding, four steps to complete it

first talk about the most comfortable aspect of comparing 4C devices to new devices: no need to flash Breed. Later, I flashed OpenWrt AX3000T following the Breed route: first figure out how to unlock, then flash the Undead Guide, then go to the Breed page and transfer the firmware—six steps all in one night. On the 4C side, there's an open-source vulnerability script called OpenWRTInvasion, which you can download on GitHub. It's designed specifically for 4C, 4A 100Mbps, and 3Gv2 old machines. After running it once, it opens the system's telnet door, leaving the rest of the road completely flat.

the entire process consists of four steps. I write in the order I walk:

Step one: Uninstall the components. Don't run scripts just yet; check the firmware version in the backend. The official OpenWrt Wiki provides a reference version of 2.14.80, which is too new, so the firmware might patch the vulnerability. The one I received starts with 2.30. First, go to the manual upgrade page in the backend, select local upgrade, and import the 2.14.80 bin file to downgrade. The downgrade method the same as manually upgrading the firmware—it's just the file is selected from an older version.

the second step, run a script and enable telnet. Connect your computer to 4C WiFi, download the script on GitHub, install Python3 and two dependencies, run the remote_command_execution_vulnerability.py, it will ask for your router address and background password. After you fill it out, wait for it to finish. At this point, telnet 192.168.31.1, username root, no password needed. When you see the phrase "are u ok," it means you are already deep in the system.

Step three: Backup. This is the step I most want to emphasize: don't skip it. After entering telnet, first use the dd command to export the entire flash image to the /tmp directory, then use SCP to pull the image back to the computer and store it. Backups are useless in daily life, but when something happens, they're the only remedy for regret.

Step 4: Brush. SCP speaks the OpenWrt firmware to /tmp, then writes a mtd command to specify the firmware partition, and the machine automatically restarts. After rebooting, the management address changes from 192.168.31.1 to 192.168.1.1. You need to manually change the network segment on your computer's network card to access the backend. The first time you log into LuCI, set the password, and then you've graduated from these 4C systems. There are all the online tutorials on command details, how to choose firmware. I've written about this kind of general knowledge before so I won't go into detail here.

I've written down all three pitfalls for you

process isn't difficult; there are indeed a few pitfalls, and I either ran into them myself or almost gave feedback.

first pitfall is the firmware version. I mentioned above that it will be downgraded to 2.14.80. This isn't for ritual, it's about the script really choosing the version. The first time I tried to save trouble, I ran the firmware version 2.30 I had just gotten. The script got an error halfway through, and it took me a few minutes to realize I should downgrade first. After lowering it, run again and clear it in one go.

second pitfall is the flash memory batch, which is the most problematic. Someone on GitHub reported that different batch of 4C uses different flash memory models. Some uncompatible firmware restarts repeatedly after flashing, and no one can save it. In the end, they have to disassemble and wire TTL wiring. So before flashing, I specifically went to the firmware release page to read the compatibility instructions from the beginning, and only dared to make a move after confirming that the flash memory model supported my device was supported. Even if it really comes to that point, don't panic—the machine costs 30 yuan, which is the tuition cap I mentioned.

The third pitfall is the space after farming. 16MB of flash sounds impressive, but once the OpenWrt system is installed, the remaining space is instantly depleted. Don't even think about the bulky plugins like AdGuard Home. Go advertise the lightweight approach of installing a block list on dnsmasq, which is sufficient. 64MB of RAM is just as precious. Installing too many plugins makes booting difficult, so I only kept the most basic features—clean and refreshing. The positioning of this machine means it's just for hands-on practice and light work—don't expect a small horse to pull a big cart.

a quick reminder: 4C doesn't have USB ports, so if you want to flash and plug in a USB drive as a download device, you can give up early.

After practice, don't throw it away: The three positions I assigned to it

after practicing 4C, I didn't throw it into the drawer; only by squeezing every last drop of 30-yuan stuff can you truly live well. After thinking it over for several days, I assigned it three positions.

first position: Portable Router for Business Trips. This is the scenario I use most: stuffing 4C into my laptop bag takes up no space, plugging the internet cable into the hotel and connecting both laptop and phone to it. There are two advantages: first, my phone doesn't need to connect directly to the hotel's public WiFi, with my own router in between; Second, I have the final say about DNS, the hotel's network hijacking pop-up little tricks almost completely disappeared from me. There are no weaknesses in this scenario for 100Mbps ports, and very few hotels have broadband exceeding 100Mbps.

second position: emergency backup machine. On the night the main router at home really failed, the 4C connected for the whole night, enough for dialing up the internet and sending an email, and then calmly studying the main power unit the next day. As a backup, it usually gathers dust, but if it can step up at a critical moment, that's considered a good deed.

third position: Intelligent Device Distribution Network Test Bench. For the newly purchased camera and socket, I first got the 4C small site to configure and test them once, confirming everything was fine before installing them into the home main network. With dozens of smart devices at home, troubleshooting is a hassle when problems really arise. Isolating the testing process outside saves a lot of trouble.

who should get one, and who should just take a detour

finally settle the accounts and take them as they are.

one more thing in the middle: if you want a long-service router next to ads, the 4C foundation is barely enough. Paying an extra 70 yuan for a Redmi AX6S 256MB of memory is four times that of a 4C processor, and the flashing ecosystem is even hotter—that's the real workload. The value of the 4C lies in 'practice,' not in 'application.' Once you understand this, spending 30 yuan is worthwhile.

the finishing order: Xianyu takes the device and checks the condition as you like, but the power supply must be → to check the backend and upgrade the firmware version→ then switch to telnet, back up first→ then start with the swap the network segment and enter LuCI → assign a position. My own order is like this: later, when I AX3000T move, I followed muscle memory and took every step to pass in one go. Buying it for 30 yuan without worry, I think this deal is worth it.