Address Resolution Protocol
Address Resolution Protocol is the important topic of the Computer Network. Moreover, freestudy9 has all kind of important information and topic related to it.
- Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP address) to a physical machine address that is recognized in the local network.
- For example, in IP Version 4, the most common level of IP in use today, an address is 32 bits long.
- In an Ethernet local area network, however, addresses for attached devices are 48 bits long. (The physical machine address is also known as a Media Access Control or MAC address).
- Moreover, A table, usually called the ARP cache, used to maintain a correlation between each MAC address and its corresponding IP address.
- Address Resolution Protocol provides the protocol rules for making this correlation and providing address conversion in both directions.
Working of Address Resolution Protocol
- 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 ARPs cache and, if it finds the address, provides it so that the packet can convert to the right packet length and format and sent to the machine.
- If no entry found for the IP address, Address Resolution Protocol 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 ARPs cache for future reference. And then sends the packet to the MAC address that replied.
- A possible ARPs table in any node is as per below
- Since protocol details differ for each type of local area network. There are separate ARPs Requests for Comments (RFC) for Ethernet, ATM, Fiber Distributed-Data Interface, HIPPI, and other protocols.