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?
ARP (Address Resolution Protocol) cache
When a device needs to send a packet to a destination MAC address on a remote LAN segment, but there are no mappings in its ARP (Address Resolution Protocol) cache, it will need to perform an ARP request.
The device will send an ARP request broadcast message to all devices on the local network, asking for the MAC address associated with the IP address it wants to communicate with.
The ARP request contains the sender’s MAC address and IP address, and the target IP address for which the MAC address is being requested.
All devices on the local network will receive the ARP request message, but only the intended recipient with the matching IP address will respond.
The recipient will send an ARP reply directly to the device that sent the request, providing its MAC address. This ARP reply includes the target MAC address, completing the mapping in the ARP cache of the requesting device.
Once the device receives the ARP reply, it will update its ARP cache with the MAC address of the remote host. It can then use this MAC address to encapsulate the packet in a data-link layer header and send it directly to the destination device on the remote LAN segment.
If no ARP reply is received within a certain timeout period, the device will assume that the destination host is not reachable, and an appropriate error or timeout message may be generated.
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