one ,ARP Role of the agreement

1,ARP Protocol used in Ethernet , Used to resolve the target address of communication to MAC address , When communicating across network segments, the gateway's MAC address .

2, If computer Aping computer B Address of , First, computers A Judge the target IP Address and whether you are in the same network segment , If in a network segment , Target of data link layer encapsulation MAC Address is computer C of MAC address .

3, If computer Aping computer C Address of , First, computers A Judge the target IP Address and whether you are in the same network segment , If not in a network segment , Target of data link layer encapsulation MAC The address is the gateway MAC address .

two , Address resolution protocol ARP main points

1,ARP Request grouping : Include sender hardware address / Sender IP address / Target hardware address ( Fill in when unknown 0) / Target party IP address .

2,ARP The request is sent to a broadcast address ( Router does not forward ARP request ).

3,ARP Response grouping : Include sender hardware address / Sender IP address / Target hardware address / Target party IP address .

4,ARP Packets are encapsulated and transmitted in frames of the physical network .

three , Address resolution protocol ARP Working process of

When the host A To send a message to a host on this LAN B send out IP Datagram time , First in its ARP Check whether there are hosts in the cache B of IP address .

1. if there be , You can find out the corresponding hardware address , Then write this hardware address to MAC frame , Then, the MAC The frame is sent to this hardware address .

2. If not ,ARP The process broadcasts and sends a ARP Request grouping . received ARP After response grouping , Will get IP Address to hardware address mapping write ARP In cache .

four , summary

1,ARP Used to solve the problem of host or router on the same LAN IP The mapping problem between address and hardware address .

2, If the host you are looking for is not on the same LAN as the source host , Then we have to pass ARP Find the hardware address of a router on this LAN , Then send the packet to the router , Let this router forward the packet to the next network , The rest of the work will be done by the next network .

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