The Address Resolution Protocol (ARP) is a fundamental protocol used in IP networking to map a device's IP address to its corresponding Media Access Control (MAC) address. This mapping is essential for enabling communication within a local network segment.
How ARP Works:
* ARP Request:
* When a device (Host A) needs to communicate with another device (Host B) on the same local network, it checks its ARP cache to see if it already has Host B's MAC address corresponding to its IP address.
* If the MAC address is not in the cache, Host A broadcasts an ARP request packet to all devices on the local network. This packet includes Host B's IP address and requests the MAC address associated with that IP.
* ARP Reply:
* Upon receiving the ARP request, the device with the matching IP address (Host B) responds with an ARP reply. This reply is sent directly to Host A and contains Host B's MAC address.
* Updating ARP Cache:
* Host A receives the ARP reply and updates its ARP cache with the new IP-to-MAC address mapping. This cached information allows for efficient communication without the need for repeated ARP requests.
Key Functions of ARP:
* IP to MAC Address Resolution:
* ARP's primary function is to resolve IP addresses to MAC addresses, enabling devices to locate each other on the same local network segment.
* Facilitating Data Link Layer Communication:
* By providing the necessary MAC address, ARP allows data packets to be correctly addressed and transmitted over the network's data link layer.
Clarifications on Other Options:
* Option B: Discover directly connected neighbors
* This function is typically performed by protocols like the Neighbor Discovery Protocol (NDP) in IPv6 or by network discovery tools, not by ARP.
* Option C: Build and maintain switch MAC tables
* Switches build and maintain MAC address tables by observing the source MAC addresses of incoming frames, a process independent of ARP.
* Option D: Resolve host name
* Resolving hostnames to IP addresses is the function of the Domain Name System (DNS), not ARP.
References:
* Understanding ARP (Address Resolution Protocol)
* How ARP Works