1、ARP Address resolution protocol , It is based on ip Address get the physical address of the host in the LAN .
2、ARP working principle （ The process ）：
① Two terminals in the LAN need to communicate , terminal A To the terminal B Send a message , Through a data encapsulation of each layer .
② When encapsulated in the data link layer , If the terminal A Of ARP There are no terminals in the address table B Of mac Address information , Then there will be a ARP Broadcast of .
③ Target host received arp When asked , I will take my own mac Fill in the corresponding to the source host , At the same time, the corresponding mac Information is recorded in your own arp In the address table .
④ The source host gets the destination host's mac Address . After the acquisition, the corresponding purpose mac Fill in and send the information to the destination host .
3、 If the destination host is not in the same network segment , Then set the goal mac Set to gateway mac. The gateway gets this data frame , Check the purpose mac Is your own , In view of the purpose ip, Check out your ip Address table , The next jump mac The address is the destination address , To his own mac The address is the source address .
4、ARP Deception and attack ：
①ARP The attack only makes the LAN or a terminal in the LAN unable to communicate with the external network or other terminals .
principle （ Reactive spoofing ）： Hackers forge ARP message , Tell the source host that a fake one does not exist mac Address , The source host then sends the message to the non-existent destination host , So as to realize network interruption , Unable to communicate .
principle （ Broadcast deception ）： Hackers forge ARP message , Broadcast ARP Tell all hosts in the LAN ,ARP Source MAC Is a nonexistent mac, And the source IP Gateway Based IP, That is, tell all hosts a nonexistent gateway address , Make all hosts unable to access the network .
ARP The attack just made the LAN unable to communicate , There will be no big loss .
②ARP Cheating is forging a ARP The message tells other hosts that they are the destination host , In this way, other hosts will send all messages to hackers .
principle （ Reactive spoofing ）： Tell the source host , He is the target host he is looking for , To his own mac Tell the source host , In this way, the source host will send the message to the hacker .
principle （ Broadcast deception ）： radio broadcast ARP message , Tell all hosts in the LAN , I am the gateway , Then the communication between all hosts in the LAN and the external network will be sent to the hacker here .
ARP Cheating can lead to risks such as information disclosure , Caused substantial damage .
