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At the high-speed rail station, I connected to free WiFi, and a young man next to me asked if I was afraid of being exposed. When I got back, I treated my computer like a bystander on the same web and did a thorough inspection: HTTPS locked passwords and text tightly, but DNS asking for directions, a shout in a handshake, and websites still running http—these three were truly exposed. There are only four items on the self-protection list, and ninety percent of people don't know about the last one....

After changing the router's DNS, I wanted to verify if it was valid. I typed nslookup, and the server line showed 192.168.31.1, not the 223.5.5.5 I typed. Below it was a line of non-authoritative response, and both places seemed to be errors. Actually, it's all normal output: the router acts as a middleman, not authoritative, just recalling the cache. I used my own domain name to ask for authoritative information, three public DNS providers, and the 114 detection code one by one, with a human translation for every line output....

The hosts file is the address book your computer keeps on its own, placed before DNS; some domains inside are used directly, without even asking the DNS server. I tested that adding one line takes effect immediately, no need to restart. I used it to block websites, record house numbers for my home NAS, and even helped colleagues dig through a colleague's computer to extract a three-line hacking record of a Trojan secretly inserted—all in one minute....

In the two seconds after entering the password for WiFi, the router and phone shook hands four times: the password was never online and the person who caught the packet couldn't get it. But weak passwords can still be cracked by dictionaries. I tested it on my own computer and finally figured out why the master key connects to your home....

During the New Year, the first thing relatives asked when they came in was to ask for the WiFi password. The elderly lady repeated it three times, and some people still entered it incorrectly. I made a QR code for my mother-in-law's family and stuck it on the fridge. After scanning, it connected in two seconds. This code isn't an image, just a line of characters. You can use a generator yourself and make one in five minutes. If you can't scan it on WeChat, it's normal to blame the code....

When you open the WiFi list in a new place, a string of names appears every second or two. This is done by the division of labor between the phone and the router: every 0.1 seconds, the router broadcasts a beacon frame to announce the door, and the phone sends questions to each channel. Where the signal grid comes from, why hidden WiFi is still detected, why does phone scanning require location permissions—all are hidden within this mechanism....

netstat -ano is a built-in Windows connection viewing command. Each column—protocol, local address, external address, status, and PID—has its own details. With just one command, you can clearly see who your computer is communicating with. All five TCP states are translated into plain language. Don't shout 'get caught by the big screen' of external IPs, distinguish the difference between TIME_WAIT and CLOSE_WAIT at once, and there's also a 0.0.0.0 and 127.0.0.1 listening trick that 90% of people haven't noticed....

The web page was as slow as dialing; tracert typed out a dozen lines, a string of IPs with a row of asterisks, looking like the network was cut in half. Actually, the first jump is your own router. The 100.64 line is the carrier's main gate, and the asterisk usually means the router is too lazy to respond. I followed Alibaba DNS from inside the house and ran two search methods, explaining each line clearly what it meant and what a real broken road looked like....

Laptop WiFi is slow, and trying to guess signal bars over the phone is useless. Windows comes with a built-in command netsh wlan show interfaces. Signal percentage, negotiation rate, channel, and bandwidth are all on this screen. The root cause of my old Sun's laptop getting stuck at 200MB is that I had him type this line and it would see clearly....

When the home network is disconnected and you call for repair, the technician's first line is to type in ipconfig and read the output to him. What are the IPv4 addresses, default gateways, DHCP server, and DNS server responsible for? What bad signals starting with 169.254 are? I checked the output line by line. From now on, when you disconnect from the internet, check the three lines yourself, then call again—it's not too late....