Saturday, 8 April 2017

Reaching to an end-system

Reaching to an end-system

We are all familiar with the domain name and the IP addressing, when we access any website on internet we call by its name called “domain name”, the domain name is then converted to IP address for accessing that system. But IP address alone is not sufficient; we also need the physical address (MAC address) of the system. As it is not possible for a source system to know the physical address of all the destinations, the Address Resolution Protocol (ARP) was developed to enable communications on an internetwork. Layer 3 devices need ARP to map IP network addresses to MAC hardware addresses so that IP packets can be sent across networks.
Before a device sends a datagram to another device, it looks in its ARP cache to see if there is a MAC address and corresponding IP address for the destination device. If there is no entry, the source device sends a broadcast message to every device on the network. Each device compares the IP address to its own.
Only the device with the matching IP address replies to the sending device with a packet containing the MAC address for the device. The source device adds the destination device MAC address to its ARP table for future reference, creates a data-link header and trailer that encapsulates the packet, and proceeds to transfer the data. The figure below illustrates the ARP broadcast and response process

By Ravinder Nath Rajotiya
HOD, Electronics and Communication Engineering Department,
JEMTEC, Greater Noida

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