ARP

ARP the network layer Protocol, designed to determine the MAC address for known IP address, that is, the Protocol takes the responsibility of translating an IP address to the MAC address. The Protocol itself went from the reference model OSI, however, full compatibility with TCP/IP the Protocol brought to a new level of use.

The principle of operation

There are two modes ARP: ARP request and ARP reply. The sender using ARP query asks for physical (MAC) the address of the recipient.

 The process of data packet transmission network layer through the Ethernet segment, the network stack checks the ARP cache, to find out, does it already need information about the recipient. If such an entry in the ARP cache is missing, it performs a broadcast ARP request. This inquiry has the following form: "Does anyone know the physical address of the device, with the following IP address?"When the recipient with the same IP address will take this package, we will have to respond: "Yes, this is my IP address. My physical address next: ..." After that, the sender will update its ARP cache and will be capable of transmitting information to the recipient. The entries in the ARP cache can be static or dynamic.

Usually, the entries in the ARP table, created dynamically, remain in the cache for 2 minutes. If during those two minutes occurred retransmission of the data at this address, the retention time of the cache entry is extended by 2 minutes. This procedure can be repeated until, while the entry in the cache will exist until 10 minutes. After that, the record will be deleted from the cache, and will be re-sent ARP request.

RARP

RARPis also a network layer Protocol model OSI, which performs a reverse mapping of addresses, that is, converts the physical (MAC) address IP-address.

The Protocol used during the boot node, when he sends a group request with your physical address (MAC). The server accepts this request and looks through its tables in search of the appropriate physical, IP-address. After the discovery address is sent back to the requesting node. Other servers, nodes can also listen to this dialogue and to locally store this information in their ARP-tables.

RARP allows you to split IP-address not often used between the host nodes. After using any unit IP-he could be released and granted to another node.

RARP is a Supplement to ARP.