RARP：Reverse Address Resolution Protocol

RARP:Allows the LAN's physical machine to request its IP address from the gateway server's  ARP  table  or  cache.   The network administrator creates a table in the LAN gateway router to map the physical address (MAC) and its corresponding IP address. When setting up a new machine, its RARP client program needs to request the corresponding IP address from the RARP server on the router. Assuming a record has been set up in the routing table, the RARP server will return the IP address to the machine.

Cause

ARP (address Resolution Protocol) is a protocol in which a device obtains a physical address that it does not know through its own known ip address. If a device does not know its own ip address, but knows its own physical address, this is the case with diskless workstations on the network, all the device knows is the physical address on the network interface card. What should I do in this case? RARP works in the opposite way to ARP. The rap issues a physical address to be reverse-resolved and wishes to return its corresponding ip address, which includes the ip address issued by the rap server capable of providing the required information. Although the sender issues broadcast information, the RARP specifies that only the RARP server can generate a response. Many networks specify multiple RARP servers, both for balancing loads and for backup as a problem.

Operational principle

1. The sending host sends a local RARP broadcast in which the own MAC address is declared and any RARP server receiving the request is requested to assign an IP address ;

2  After receiving the 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 it exists, 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 this;

5  The source host receives the response information from the RARP server and communicates with the obtained IP address; if the response information from the RARP server has not been received, the initialization failed.

working process

1  Each device on the network will have a unique hardware address, usually the mac address assigned by the device manufacturer. PC1 reads the MAC address from the network card, and then sends a broadcast packet requested by RARP on the network to request the RARP server to reply to the IP address of the PC.

2  The RARP server receives the RARP request packet, assigns the IP address to it, and sends the RARP response to the PC1 .

3  When PC1 receives the RARP response, it communicates with the obtained IP address.