Address
Resolution Protocol ARP and RARP
IP addresses are assigned independently
of the hardware addresses of the machines. To send a datagram on the Internet,
the network software must convert the IP address into a physical address, used
to transmit the frame.
Address resolution refers to the
determination of the address of a device from the address of that equipment to
another protocol level. We solve, for example, an IP address in an Ethernet
address or an ATM address.
It's ARP (Address Resolution Protocol)
performing this translation between the IP world and Ethernet based on the
physical network. ARP enables machines to resolve addresses without using
static table that lists all addresses of both worlds. A machine uses ARP to
determine the recipient's physical address by broadcasting an ARP request to
the subnet containing the IP address to be translated. The machine with the
relevant IP address responds with its physical address. To make ARP more
efficient, each machine maintains in memory a table of addresses resolved and
thus reduces the number of Broadcast emissions.
At the time of initialization
(bootstrap), a mass storage without the machine (diskless) should contact their
server to determine its IP address and to use the TCP / IP services.
RARP(Reverse ARP) allows a machine to use its physical address to determine its
logical address on the Internet. The RARP mechanism allows a computer to be
identified as a target on the network by broadcasting a RARP request. The
servers receiving the message examine their table and meet. Once the IP address
obtained, the machine stores it in memory and no longer uses RARP until it is
reset.
The ARP protocol is based on the
physical network to perform address translation. To determine the recipient's
physical address, a machine broadcasts an ARP request on the subnet that
contains the IP address to be translated. The machine with the relevant IP
address responds with its physical address. This process is illustrated in Figure.
Inversely, a station that connects to
the network can know its own physical address without an IP address. Upon
initialization, the machine will contact the server to determine its IP address
and can use the TCP / IP services. RARP allows him to use his physical address
to obtain its logical address on the Internet. Through the RARP mechanism, a
station can be identified as a target on the network by broadcasting a RARP
request. The servers receiving the message examine their table and meet. Once
the IP address obtained, the machine stores it in memory and no longer uses
RARP until it is reset.
In IPv6, ARP and RARP are
replaced by a neighbor discovery protocol called Neighbor Discovery (ND), which
is a subset of the control protocol ICMP (Internet Control Message Protocol).
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