Full form: Address Resolution Protocol
Also known as: Address Resolution Protocol
Quick Definition
A Layer 2/3 protocol that maps known IP addresses to unknown MAC addresses.
ARP resolves a known IP address to its corresponding MAC address on the same local network. A device sends an ARP broadcast ('Who has 192.168.1.1? Tell 192.168.1.10') and the device with that IP responds with its MAC address. The reply is cached in the ARP table for a configurable time. Without ARP, a host cannot build the Layer 2 Ethernet header needed to deliver a packet on the local segment.
show ip arp
PC1 wants to send a packet to PC2 (192.168.1.2) on the same subnet. PC1 checks its ARP cache, finds no entry, broadcasts an ARP request, and PC2 replies with its MAC address. PC1 can now send the frame directly.
ARP is only used within the same subnet. When a device communicates with a host on a different subnet, it ARPs for the default gateway, not the remote host.
A 48-bit hardware identifier burned into every network interface card.
The IP address of the router a host sends packets to when the destination is on a different subnet.
A switch security feature that validates ARP packets using the DHCP Snooping binding table to prevent ARP spoofing.
ARP resolves a known IP address to its corresponding MAC address on the same local network. A device sends an ARP broadcast ('Who has 192.168.1.1? Tell 192.168.1.10') and the device with that IP responds with its MAC address. The reply is cached in the ARP table for a configurable time. Without ARP, a host cannot build the Layer 2 Ethernet header needed to deliver a packet on the local segment.
ARP is only used within the same subnet. When a device communicates with a host on a different subnet, it ARPs for the default gateway, not the remote host.
PC1 wants to send a packet to PC2 (192.168.1.2) on the same subnet. PC1 checks its ARP cache, finds no entry, broadcasts an ARP request, and PC2 replies with its MAC address. PC1 can now send the frame directly.
ARP falls under the Network Fundamentals domain of the 200-301 exam. Understanding it in context with related terms like mac-address and default-gateway is essential for answering scenario-based questions correctly.