Explain the process of ARP in mapping an IP address to a MAC address when a client wants to communicate with a web server on the same subnet.
Address Resolution Protocol (ARP) is a fundamental protocol in computer networking used to map an Internet Protocol (IP) address to a Media Access Control (MAC) address. When a client desires to communicate with a web server on the same subnet, the ARP process plays a important role in facilitating this communication by resolving the MAC address associated with the IP address of the destination.
The ARP process starts when the client, let's say with IP address 192.168.1.2, needs to send data to a web server with IP address 192.168.1.3. Since the client and the web server are on the same subnet, the client first checks if the destination IP address is within its subnet. Subnets are defined based on the IP address and subnet mask configuration. If the IP address is on the same subnet, the client knows that it can directly communicate with the destination device without involving a router.
In this scenario, the client checks its ARP cache, a local table that stores mappings of IP addresses to MAC addresses of devices recently communicated with. If there is no entry for the destination IP address in the ARP cache, the client initiates an ARP request to resolve the MAC address associated with the IP address of the web server.
The client broadcasts an ARP request packet to all devices on the local network, asking "Who has IP address 192.168.1.3? Please send me your MAC address." This broadcast is necessary because the client does not yet know the MAC address of the web server. By broadcasting the request, the client ensures that the intended recipient, in this case, the web server, will receive the ARP request.
Upon receiving the ARP request, all devices on the local network examine the IP address in the request. The device with the matching IP address, in this case, the web server with IP address 192.168.1.3, replies with an ARP reply packet containing its MAC address. This reply is unicast, meaning it is sent directly to the client that initiated the ARP request.
The client receives the ARP reply packet, which includes the MAC address of the web server. The client then updates its ARP cache with the mapping of the IP address 192.168.1.3 to the MAC address of the web server. This caching of ARP entries helps improve network efficiency by reducing the need for frequent ARP requests.
With the MAC address of the web server now known to the client, it can encapsulate the data intended for the web server within Ethernet frames. These frames contain the MAC addresses of both the client and the web server, ensuring that the data reaches the correct destination at the data link layer of the OSI model.
The ARP process involves broadcasting ARP requests to resolve the MAC address associated with a destination IP address on the same subnet. By mapping IP addresses to MAC addresses, ARP enables devices to communicate effectively within a local network.
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