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dineshb_2001

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ARP,RARP

Please can anyone describe for me what is a ARP, RARP and where and in which way they are useful.

Please don`t mention the definition used in Webopedia. I studied them but didn`t got the exact point. Please describe them in detial.

thanks in advance.
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Lee W, MVP
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A MAC address is something like an electronic serial number.  Whenever info is sent from your computer, the packet contains the MAC Address.  ARP (Address Resolution Protocol) resolves the MAC address to an IP Address.  In a sense this identifies the calling computer connecting to your computer.  Think of it in terms of a car - the MAC is like a Vehicle Identification Number (VIN) and the license plate like an IP Address.  You can easy change the license plate and pass it to someone else, in theory, you can't do that easily with the VIN/MAC address.

RARP is simply the reverse of ARP.  It effectively finds the MAC address of the device with an IP Address.

It's important to note that network switches and routers can mask the correct MAC address of something as they can effectively replace it with their own as the packet travels through them
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shaolee

from the CCNA-

The Address Resolution Protocol (ARP) is an Internet layer protocol that helps TCP/IP devices find other devices in the same broadcast domain. ARP uses a local broadcast to discover neighboring devices. Basically, ARP resolves an IP address of a destination to theMACaddress of the destination on the same data link layer medium. Remember that for two devices to talk to each other in Ethernet, the data link layer uses MAC addresses to differentiate the machines on the segment. And that when devices talk to each other at the data link layer, they need to know the destination’s MAC address.


RARP-
RARP is sort of the reverse of an ARP. In an ARP, the device knows the layer-3 address, but not the data-link layer address. With a RARP, the device doesn’t have an IP address and wants to acquire one. The only address that this device has is a MAC address. Common protocols that use RARP are BOOTP and the Dynamic Host Configuration Protocol (DHCP).

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kidoman

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Hi again,

I was going through posts before mine, and I would like to contradict by saying that BOOTP and DHCP replaced the aging RARP protocol and dont use it in any way.

Regds,

Karan
ARP is a layer 3 protocol  resolves MAC Address (Hexadecimal or NIC card address or Physical address) to IPaddress or logical address.Arp mailtains a table of Mac vs Ip address called as ARP cache...............

at command prompt type arp -a   u can see what all hapens.....
RARP does the reverse of this...........

if u go in depth, allthough ARP is a layer 3 protocol it does not use an IP header, it has its own packet format and is a broadcast on the local LAN within the data field of a layer 2 frame without needing to be routed. The Ethernet Type field has the value 0x0806 to indicate an ARP.
 
Hi thribhu,

Sorry, but I think you are wrong about ARP resolving "MAC Address (Hexadecimal or NIC card address or Physical address) to IPaddress or logical address"

ARP does exactly the opposite: maps IP addresses to MAC addresses because the physical addresses are what the physical layer understands and thus mandates to be able to succesfully send the frames.

RARP obviously does the reverse but does not see the same frequency of use (if at all) as ARP does.

Kidoman
Thanks a lot.