Understanding Address Resolution Protocol (ARP) Resolution Process for Remote LAN Segments: A Comprehensive Guide

A host is trying to send a packet to a device on a remote LAN segment, but there are currently no mappings in its ARP cache. How will the device obtain a destination MAC address?

When a host wants to send a packet to a device on a remote LAN segment and there are no mappings in its Address Resolution Protocol (ARP) cache, it will need to perform an ARP resolution process to obtain the destination Media Access Control (MAC) address.

The host will first check its routing table to determine the next hop IP address or the default gateway for the remote LAN segment. It will then encapsulate the packet in a data link layer frame using the MAC address of the default gateway as the destination MAC address.

Next, the host will send an ARP request broadcast message to the local network asking for the MAC address that corresponds to the destination IP address. The ARP request message will include the sender’s MAC address, IP address, and the target IP address for which it needs the MAC address.

All devices on the local network segment will receive this ARP request message, but only the device with the corresponding IP address will respond. The device with the requested IP address will reply to the ARP request with an ARP reply message containing its MAC address.

Once the host receives the ARP reply, it will update its ARP cache with the mapping between the destination IP address and MAC address. The host will then update the destination MAC address in the data link layer frame and send it directly to the device on the remote LAN segment.

In subsequent communications to the same device on the remote LAN segment, the host will use the mapping in its ARP cache to determine the destination MAC address, eliminating the need for ARP resolution again unless the cache entry expires or is cleared.

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