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IT Interview Questions:How ARP Works ?
Information Technology (IT) Interview Questions and Answers
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IT Interview Questions:How ARP Works ?
When an incoming packet destined for a host machine on a particular local
area network arrives at a gateway, the gateway asks the ARP program to find a
physical host or MAC address that matches the IP address. The ARP program
looks in the ARP cache and, if it finds the address, provides it so that the
packet can be converted to the right packet length and format and sent to the
machine. If no entry is found for the IP address, ARP broadcasts a request
packet in a special format to all the machines on the LAN to see if one
machine knows that it has that IP address associated with it. A machine that
recognizes the IP address as its own returns a reply so indicating. ARP
updates the ARP cache for future reference and then sends the packet to the
MAC address that replied.
Since protocol details differ for each type of
local area network, there are separate ARP Requests for Comments (RFC) for
Ethernet, ATM, Fiber Distributed-Data Interface, HIPPI, and other protocols.
There is a Reverse ARP (RARP) for host machines that don't know their IP
address. RARP enables them to request their IP address from the gateway's ARP
cache. RARP (Reverse Address Resolution Protocol) is a protocol by which a
physical machine in a local area network can request to learn its IP address
from a gateway server's Address Resolution Protocol (ARP) table or cache. A
network administrator creates a table in a local area network's gateway
router that maps the physical machine (or Media Access Control
MAC address) addresses to corresponding Internet Protocol addresses. When a
new machine is set up, its RARP client program requests from the RARP server
on the router to be sent its IP address. Assuming that an entry has been set
up in the router table, the RARP server will return the IP address to the
machine which can store it for future use.
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