An Internet cable makes the whole dormitory building quieter after lights out

He tells the story of how he used an internet cable to trick his roommate. From a product perspective, the demand analysis, hands-on practice, and subsequent product iterations are impeccable, achieving the best results at the lowest cost, which is perfect.

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The only drawback is that there are not many keywords. Although it is impressive, it still took a lot of effort to find the original text. Share it with you.

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[Funny story] An attack launched by a network cable (from Blog Garden)

cause

Not long after I entered college, I encountered a headache.

The rich second generation bring laptops with them when they first arrive, which makes us losers who can only play with mobile phones envious and jealous.

The terrible thing is that there was a power outage at night but the internet was not disconnected, so the laptop could still be used after turning off the lights. Unfortunately, there was also one in our dormitory.

Often after turning off the lights, he would not stop until all the batteries were used up. He would chat and play music while playing games, which was very tormenting. Although he changed after being persuaded, he would return to his old ways after a few days.

In order to change this situation urgently, but not wanting to argue with the new classmates, I decided to use a technical solution.

Selection

But at that time, the only asset I had was a Nokia slider phone. Without equipment, everything else was just empty talk.

The only feasible way is to secretly set up a scheduled task on his computer to automatically shut down at night. But if he is discovered, it will be even worse, and there is no technical content at all.

I have no choice but to turn my attention away from the computer and onto the Internet. If I can't get online, even if I can use the computer, I won't stay up late playing stand-alone games.

Since his network cable jack was working when he first arrived, I guess my jack also has a signal. The previous class must have had it turned on, so it wouldn't be blocked after they left.

One day when no one was in the dormitory, I dragged the laptop's network cable to my side and tried it. Sure enough, there was a signal! I immediately became excited and felt hopeful!

Maybe you will say, it is impossible to connect the Internet cable to the Nokia and then use some spoof software ~ Of course it is impossible, the mobile phones at that time were not so advanced.

In fact, we don't need any software, and we don't even need any hardware, except for an Internet cable.

Demonstrate feasibility

To talk about how to use network cables, we can start from the day when we installed the set-top box a year ago.

There was a time when digital TV became popular in many cities. We were no exception, giving away set-top boxes door to door and installing them for free. Wasu TV is originally a company with Netcom, so digital TV of course shares Netcom's broadband.

Since I had already activated Netcom, I needed to connect the set-top box to the Internet. I thought I would need at least a switch. However, when the installer came in, he didn't take out a switch or even a hub. Instead, he cut the network cable with a pair of scissors!

I was shocked at the time. What on earth was going on? Although I had some understanding of network link protocols and had written some free Internet access programs using WinPCap, I knew nothing about the physical layer.

The technician said calmly that only four network cables were needed, and the rest were just for spare. So he removed four cables from the previous ones for the set-top box.

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This was beyond my expectation. I was able to connect the set-top box without using any equipment! So, I started to have wild ideas again. . .

Are these two branches two independent users from the switch's point of view? If they are connected together, will the effect be the same as plugging one line into two ports? Can it short-circuit the LAN in the same way?

I tested it with excitement, and it really worked! It really brought down the network of the entire community!

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After the recovery, I couldn't dial the number for a long time. I found many neighbors were also dialing the number through the sniffer. Apparently, the two 4-wire cables just connected also forwarded the external STP packets, resulting in the community network being isolated from the outside.

This day, I changed my previous view. It turns out that a VLAN storm can occur with just one network cable!

Why does a storm occur when a network cable is plugged into two ports of a switch? Because the switch will forward packets sent to the broadcast address to all interfaces. If there is a loop between two interfaces, once a broadcast packet appears, it will be sent to each other in a loop, exhausting the bandwidth of the entire device. Don't underestimate the switch, it is designed for packet transmission. The storm can fill up each interface and consume the backplane bandwidth. The STP protocol is designed to solve this problem and perform loop detection.

Although I learned this new skill, the knowledge at the physical level was basically useless and I forgot about it - until I came to university and found a signal under my seat in the dormitory.

Design MVP

According to my recollection, we played LAN games among the dormitories. Obviously, this was not an independent network segment, so I was even more confident!

Immediately find an Internet cable, cut off the crystal head on one side, scrape off the outer skin, and then stick the corresponding four strands together in pairs.

Sure enough, the nearby dormitories began to hear - no, there was silence for a few seconds, followed by screams and shouts. "It's stuck!", "Who lost it?", "What's going on?", "Shit, the network is down~~~".

I ran out to the corridor and saw that the whole building was in turmoil! It turned out that this dormitory building didn't have any VLANs, and all the hundreds of dormitories were connected together!!!

At this time, I was both excited and worried. I was excited because I could capture thousands of people's traffic with a computer. I was worried because I only wanted to prank my own dormitory and didn't want to involve everyone.

But no matter what, the operation continued. At this time, there was no problem with the technology, and the only thing left was to implement it.

How to do it calmly and covertly? In order not to expose the absurdity of having an Internet cable plugged in without a computer, the wiring is laid along the covered cabinets as much as possible, from behind the wardrobe to the bed.

The remaining horizontal part is buried in the gap beside the bed and covered with a mat. If you don't look closely at the whole layout, you can't find it at all~

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Product launch

After the lights were turned off that night, the night owls began to get restless again, and I couldn't wait to start experimenting.

Like several other classmates, he pretended to play with his mobile phone, but in fact he had started to connect calls quietly, feeling like an underground intelligence agent.

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When the last wave was connected, the smooth game sound immediately became stuck. After all, the whole building is in this LAN, and the number of broadcast packets is quite large.

I can only hear the background music of the game, but no sound effects!

Thinking about the 100Mbps traffic passing through the network cable in my hand, it seemed as if I could see dense ARP and NetBIOS flashing in the darkness - and the pitifully few game data packets that were squeezed out.

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The afternoon commotion broke out again.

Although it is much less after turning off the lights, it is obviously clearer in the night environment. Most of those who were disconnected were unwilling to do so and wanted to continue playing.

This time, I didn’t plan to be so violent. If the loop detection was triggered, the whole building might be blocked. So, I changed it to connecting for a few seconds, disconnecting, connecting again, and disconnecting...

Although the game was still running, it was constantly stuck. Before long, there were waves of warm shutdown sounds, and everyone went to sleep.

The first battle was a success! I finally had a good sleep.

Improved v1

In the first few days, the effect was very ideal, and everyone went to bed early. But soon they found that the network would be restored after a while.

The reason was simple. My brother let go of the string before he fell asleep, so they started going crazy again.

It is much more difficult to reconnect the network cable when you are half asleep, and often irrelevant parts get tangled together, which results in no effect.

Therefore, an improvement in user experience is needed.

In fact, three of the strands are pre-glued, and you only need to control one strand. It is better to hide the three strands in advance and leave only one strand by your side, so that you will not make a mistake in connecting them.

I changed the network cable and made it again. This time, I taped three of the strands together and hid them behind the closet, leaving only one strand hanging up. The line was also much thinner.

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This is just like a circuit breaker. There are only two wires in total, just touch or separate them.

Even in your sleep, you can easily disconnect from the Internet with just a few taps!

Improved v2

However, with such simple equipment, there will always be operating errors.

In the middle of the night on a weekend, after being woken up by the all-night noise, I quickly connected to the Internet and continued to sleep.

Unexpectedly, I was so sleepy this time that I fell asleep directly.

It was not until after 10 o'clock in the morning that I was awakened by a series of rapid knocks on the door. I thought it was the classmate next door who was deliberately harassing me, but it kept going on, so I had no choice but to get up and open the door. After opening it, I found a middle-aged man with a tool bag coming in.

At this moment, I suddenly realized that I forgot to disconnect the network cable!!! It was disconnected for the whole night, and they came to check!

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There was no time to clean up, and I thought that I was finally exposed. But the chef took a quick look and found that our table was clean and there was nothing on it.

The only thing left was a laptop, which was still powered on. So I went over to unplug the network cable and left.

Luckily I escaped this disaster, but it is in urgent need of improvement. It would be ideal if it could be turned on before going to bed and automatically turned off after falling asleep. No more having to use the mind to turn it off in sleep.

So I decided to make a flexible switch that would turn on when pressed and turn off when released. This way, it would automatically turn off when the body relaxes after falling asleep.

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After some improvements, the switch was made extremely concealed: the two wires were stuffed into a sock, which was stuffed with cotton cloth or other elastic materials.

Under normal circumstances, the lines are separated, but if you press down gently, they will be connected, and they will return to normal after releasing them.

But the socks felt weird in my hands, so I hid them behind my feet. From then on, whenever there was noise at night, I would just tiptoe a little and the atmosphere around me would immediately become extra quiet.

So far, I have spent two dollars to build a device that can control the network status of thousands of people with my toes. It is such a great sense of accomplishment :)

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Soon, everyone seemed to have discovered a pattern: the Internet would be blocked if the sound was too loud, but they could not find the cause. So everyone became quiet and went online.