What is the role of the Computer Host Gateway? Suppose your name is Tom. You live in a big courtyard. Your neighbors have many friends. At the door, there is another Uncle Li who looks at the door. Uncle Li is your gateway. When you want to play with a friend in the yard, as long as you shout out his name in the yard, he will respond to you when he hears it and runs out to play with you. However, you are not allowed to go out of the door. If you want to contact the outside world, You must contact Mr. Li (GATEWAY) at the door by phone. If you want to chat with your classmate James, James lives in another yard far away, and he also has an Uncle Wang (James's gateway) in his yard ). But you don't know the phone number of James's house, but your teacher in charge has a list of all the students in your class and a phone number comparison table. Your teacher is your DNS server. So you dialed the phone number of Uncle Li at home and had the following conversation: Tom: Ye Li. Can I ask the class teacher to check James's phone number? Uncle Li: Well, you are waiting. (Then, Uncle Li Hung up a phone number for your class teacher and asked James about his phone number.) I asked him if his phone number was 211.99.99.99. That's great! Uncle Li, I want to contact James. Could you help me contact James. Uncle Li: No problem. (Then, Uncle Li sent a request to the telephone Bureau to connect Mr. Smith's phone. The last pass was, of course, transferred to Mr. Wang from the courtyard of Mr. Smith's house, then grandpa Wang transferred the phone number to Xiaoming's house.) Then you got in touch with James. As for the DHCP server, it can be used as a metaphor: there are more and more residents in your yard. The telephone switches in the transmission room, Uncle Li, cannot meet the needs of so many residents, so we had to adopt a new technology called DHCP. When the residents started the system, they randomly got a phone number, and each time they got a different number. Uncle Li at your door: Your gateway, your class teacher: The telephone switch of your DNS server transmission room: the DHCP server is the same as above, the conversation between Uncle Li and Mr. Wang is called routing. In addition, if there is another child called Tom, he lives in the courtyard to visit Uncle sun, because he has just built a dark courtyard, and Uncle sun has just arrived, he does not have the phone number from Uncle Li and Uncle Wang's office (Ye Li and Mr. Wang certainly do not have his phone number). There are two situations: qq profile pictures 1. Zhao Dama from the neighborhood committee told Sun's phone number about Uncle Li and Wang (Zhao Dama also told Li and Wang about Sun ), this is called static route configuration 2. Zhao Dama is ill. Grandpa sun calls around and says, "I am from the dark, And they call the phone in the yard ", the result was heard by Li and Wang, And he recorded it in their address book. Then Li and Wang sent a call to Grandpa sun and said, "I am James (not a little bit) they managed the phone number in the yard. "This is called Dynamic Route configuration. Then, if you don't need to look for the dark one day, the result is naturally that you don't need to call Uncle Li and say," Grandpa, I am looking for Tom "(here I omitted the process of checking the phone number by Mr. Li. Suppose he knows the phone number by Mr. Li). When Mr. Li looks for the address book:" Oh, the phone number of the yard is managed by Uncle sun. if you want to contact Mr. Sun, you must first notify him. I can notify Mr. Wang to ask him to contact Mr. Sun, you can also directly find Sun, Of course, it was convenient for me to directly find Sun. "So Uncle Li called Uncle sun and then he transferred the phone to Mr. Sun's home. Here, Uncle Li's address book is called a route table. Uncle Li chose whether to directly find Uncle sun or ask Uncle Wang to help transfer the route. The reason why Uncle Li chooses to contact uncle sun directly is that he can find Uncle sun in one step. If Uncle Wang needs to transfer the information, two steps are required, here, the "Step" is called "Number of hops". Uncle Li's choice follows the minimum step (number of hops) Principle (if he does not follow this principle, it may take some time to find the hidden state. The final result may lead to Uncle Li being fired for poor work. This is called "the delay is too long and the routing principle is unreasonable, I changed to a vro.) Of course, things always changed. I had a quarrel with James. I always called Tom these days. James thought, "Fuck, is he talking about me?" So James decided to eavesdrop on a conversation with Tom, but he was not allowed to leave the hospital. What should he do? James made such a decision: first, he told his brother Wang, who is in charge of the phone number in the courtyard, that he said, "You have called Ye Li and said that he has moved to the courtyard, I will pick up the phone number I will call him later. "Uncle Wang did not reflect it (after all, he is older !) He called Ye Li and said, "Now I have managed Mr. Sun's phone number." As a result, Mr. Li changed his address book, this is called route spoofing. In the future, if you try again, Uncle Li will transfer it to Uncle Wang (in fact, it should be transferred to Uncle Sun ), when Mr. Wang received the call, he transferred it to James (because he had already spoken to James). When James received the call, he pretended to communicate with Tom. James was a thief and was afraid to ask him in person when he met Tom tomorrow. after the communication was broken, in the name of Tom, he gave Tom a phone call to repeat what he had just said. This is called data eavesdropping. Later on, James continued to communicate with Tom, and then fell victim to James. James said, "I can't always talk to Tom like this, what should I do if I expose the stuffing one day!" So he thought of a more sinister TRICK: "I will not listen to your phone call at all. Aren't you sure you want to call me! I cannot beat you, too !", How did he do it? Let's take a look: He contacted a group of friends and colluded with them. Every day, at a fixed time, everyone made a call to the transfer room in the dark courtyard. Everything was available. As long as grandpa sun answered the phone, you will hear "thunder, rain and clothes!" "A person is born by his mother, a demon is born by his mother", "your mother's surname", etc. The head is too big to listen, the phone keeps ringing! One day, Grandpa sun couldn't help it, and shouted, "I can't help pulling !!!!", So I hung up and killed myself! This is the simplest DDoS attack. Grandpa Sun's weak psychological endurance is called "a bug in the datagram processing module". Grandpa Sun's suicide is called "router paralysis ". If it was me, I would smile at home with them, for example, telling them, "I have listened to the weather forecast for a long time, clothes have been received 10 minutes ago, "whether your mother is a man or a demon" or "have a surname with your grandmother", etc. My sound psychology is called "robust datagram processing, after Grandpa sun is paralyzed, Tom finally stops calling Tom because no matter how he calls the other party, this phenomenon is called "denial of service ", therefore, James's practice is also called "Denial of Service attack ". James finally quieted for a few days. A few days later, James's yard came up with a beautiful girl named Xiaoli, who liked her very much (what is early love at a young age !) But Xiao Li has a very handsome boyfriend, and James can't help but stare. Of course, the above principle should be followed: Lili cannot be discharged from hospital. The man wanted to make a phone call, so James was so anxious: Do you still remember grandpa Wang as the telephone manager of the yard? He can manage the phone number because he has an address book. Because two children in the same yard may be called James and cannot be distinguished by their names, there are only two items in each line in the address book: door number 1, door 1234567 (this is James's), Door 2, 7654321 (this is Lili's )...... grandpa Wang has a bad memory, but it will never be wrong. (There won't be two "Gate 2" in the same yard )? Every time I call someone else, I need to give a phone number and then use the address book to knock on the door in the yard. For example, if someone says that I am looking for "1234567", grandpa Wang compared it, if it is door 1, he will go to Door 1 and "Listen to phone". If it is "7654321", then he will go to door 2 to "Listen to phone ". The phone number here is the legendary "ip address". The room number here is the 'mac' address of the legendary NIC (the MAC address of each Nic is different, this is what the NIC manufacturer wrote to the NIC chip.) James thought, "Grandma, I don't want to bubble you if I can't bubble it." Then he started his idea of grandpa Wang's address book, after careful observation and careful preparation, he finally found out that grandpa Wang had frequent urination problems (after all, it was an old man ...), finally, in the dark and windy day of the month, grandpa Wang went to the toilet. James secretly touched the transfer room and carefully changed Grandpa Wang's address book ...... after a few days, Xiaoli's boyfriend called Xiaoli again. The phone number reported by the other party was "7654321". grandpa Wang looked at the address book and relied on: door number 1, Door 1, 1234567 (this is James's), Door 1, 7654321 (Note: This was Lili, but it was changed by James )...... grandpa Wang didn't know how to change it, so he went to the door No. 1 to find Xiao Ming. James felt this beautiful, in the tone of Xiaoli's father, he severely taught the male and male relations. Respectfully hung up the phone. Of course, Lili doesn't know how the whole thing happened... qq network name here Xiao Ming's behavior is called "ARP spoofing" (because ARP packets are sent on the actual network, it is called "ARP spoofing "), grandpa Wang's address book is called "ARP table". Note: grandpa Wang now has two address books, one of which is the book that records the phone number of each yard, which is called the "route table ", one is the current description of the detailed information in the yard, which is called the "ARP table ". There is a life statement: "People are always pursuing perfection, even if they can never do it." (remember this sentence, because this is a celebrity-that is, me) in grandpa Wang's system, one of them wrote "check the corresponding house number and phone number (ARP table) every month", which is called "Refresh ARP table ", the time limit of each month is called "the cycle of refreshing the ARP table ". In this way, James will never be able to find Xiaoli, And he will secretly change the address book once every month. But this is what he has to do! In addition, James is very smart. If the address book (ARP table) is changed to Door 1, 1234567 (this is James's) door 2, 1234567 (Note: James changed this, but he was dizzy and wrong )...... the computer will pop up a dialog box prompting "Duplicate IP addresses". In the end, grandpa Wang will be overwhelmed, so he will notify Door 1 and door 2 that your phone number is repeated. In this way, Lili will know that someone is destroying her good deeds. This phenomenon is called "a scam has been exposed." Tom knows that James eavesdropped on his phone number with Tom, so we agreed on the password with Tom. Click "encrypt" at home and then tell "dark. Tudou-> Wednesday, sweet potato-> treat, dumb-> small family. So I told Tom: potato dummies. James listened ??? Don't understand .... Depressed... This is encrypted. In addition, Lili also knew that James had changed his phone number. So grandpa Wang went to the door and wrote down the phone number and house number one by one. In addition, attackers are not allowed to modify the password. They can only have their own keys (passwords ). This is the binding between the IP address and the MAC address. When someone changes the phone number, he needs to change it to grandpa Wang. The trouble is troublesome, but it is safe. But James secretly stole grandpa Wang's key (the password was stolen), so he could modify it. That's it.
