Shulou(Shulou.com)06/01 Report--

Address Resolution Protocol, or ARP (Address Resolution Protocol), is a TCP/IP protocol that obtains physical addresses based on IP addresses. When sending information, the host broadcasts the ARP request containing the target IP address to all hosts on the network, and receives the return message to determine the physical address of the target; after receiving the return message, the IP address and the physical address are stored in the local ARP cache and retained for a certain period of time, and the next request directly queries the ARP cache to save resources. The address resolution protocol is based on the mutual trust of the hosts in the network. The hosts on the network can send ARP reply messages on their own. When other hosts receive the reply message, they will record it in the local ARP cache without checking the authenticity of the message. In this way, the user can send a pseudo ARP reply message to a host, so that the information it sends cannot reach the expected host or the wrong host, which constitutes an ARP spoofing. The ARP command can be used to query the correspondence between IP address and MAC address in the native ARP cache, add or delete static correspondence, and so on.

Examples of ARP workflows:

The IP address of host An is 192.168.1.1 and the MAC address is 0A-11-22-33-44-01.

The IP address of host B is 192.168.1.2 Magi MAC address is 0A-11-22-33-44-02

When host A wants to communicate with host B, the address resolution protocol can resolve the IP address (192.168.1.2) of host B to the MAC address of host B. the following is the workflow:

(1) based on the contents of the routing table on host A, IP determines that the forwarding IP address used to access host B is 192.168.1.2. Host A then checks the matching MAC address of host B in its own local ARP cache.

(2) if host A does not find a mapping in the ARP cache, it asks for the hardware address of 192.168.1.2 and broadcasts the ARP request frame to all hosts on the local network. Both the IP address and the MAC address of source host An are included in the ARP request. Each host on the local network receives an ARP request and checks to see if it matches its own IP address. If the host finds that the requested IP address does not match its own IP address, it discards the ARP request.

(3) if host B determines that the IP address in the ARP request matches its own IP address, it adds the IP address and MAC address mapping of host A to the local ARP cache.

(4) Host B sends an ARP reply message containing its MAC address directly back to host A.

(5) when host A receives an ARP reply message from host B, the ARP cache is updated with the IP and MAC address mappings of host B. The native cache has a lifetime, and the above process will be repeated again when the lifetime is over. Once the MAC address of host B is determined, host A can send IP communications to host B.

The inverse address resolution protocol, namely RARP, is relative to the ARP protocol, which translates the physical address of a host in the local area network into an IP address. For example, if there is a host in the local area network that only knows the physical address but does not know the IP address, then the broadcast request for its own IP address can be sent through the RARP protocol, and then the RARP server will be responsible for answering.

RARP protocol workflow:

(1) send a local RARP broadcast to the host, in this broadcast packet, declare your own MAC address and request any RARP server that receives the request to assign an IP address

(2) after receiving this request, the RARP server on the local network segment checks its RARP list to find the IP address corresponding to the MAC address.

(3) if present, the RARP server sends a response packet to the source host and provides the IP address to the other host for use

(4) if it does not exist, the RARP server does not respond to it.

(5) when the source host receives the response information from the RARP server, it uses the obtained IP address to communicate; if it has not received the response message from the RARP server, it indicates that the initialization failed.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.