Address Resolution Protocol - Intro

Network layer protocols Contents Introduction Address Resolution Address Resolution Protocols

Network Layer The Network Layer is responsible for end-toend (source to destination) packet delivery including routing through intermediate hosts.

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Introduction Transporting packets of data within IP-based n/w requires two levels :  Logical  Physical

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Logical address It is an Internetworking address, as it is globally unique and universally accepted. It is necessary for transporting data between two devices across the Internet

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Physical Address Physical network, each devices is identified with a locally unique physical address that is embedded in the hardware called Network Interface Card (NIC) Also called as Ethernet Hardware Address (EHA), hardware address, adapter address, or physical address. #

Address Resolution Mapping an IP address to a Physical address

Two types Static • • • •

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Dynamic

Created and updated manually on • each machine Physical Address stored in NIC NIC in a machine changed, Physical address also changed In some LAN the IP address changes every time while powered up (Ex: Local Talk, Apple Talk) • If we used the DHCP to assign the IP, the address will be changed • each time In portable computer the IP address changes every time

Whenever a machine knows either the physical or the logical address of another host, it can use an address resolution protocol(ARP) and reverse address resolution protocol(RARP) ARP – mapping of IP to physical address RARP – mapping of physical address to IP #

Have

Destination IP Address 75.15.125.4

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Need Resolved (mapped) to

Destination Physical Address 00 00 0C 00 23 45

ARP is used to resolve the physical address of the destination device from its IP Host of the network transmits the query packet onto the local network to find the physical address Query packet includes broadcast address like FF FF FF FF FF FF All the host will receive the query only the intended addressed host can resolve the query and reply to the requested host

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Has Destination IP address; needs Physical address of the host

Network 200.40.8.0

Does anyone out there know the Physical address for host 200.40.8.6..? 200.40.8.1

Host B

Host C

200.40.8.2

200.40.8.3

Host D

200.40.8.4

Host A

ARP broadcast from host A onto local network 200.40.8.6 Yes, my IP address Is 200.40.8.6, & My Physical Address is 00 0C 2B 11 44 66

200.40.8.5

Host E

200.40.8.6

Host F

200.40.8.7

Host G

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ARP Cache • The host responds to the ARP request with an ARP reply, which contains its logical address as well as its local (hardware) address(00 0C 2B 11 44 66) • Host A maps host F’s IP and physical address and stores both of them in a location in volatile RAM called ARP Cache. #

Any Questions..??

tHaNk YoU..

Seminar by Nilofer