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What devices use ARP?

Published in ARP Devices 3 mins read

Devices that utilize the Address Resolution Protocol (ARP) include hosts and certain network devices that operate at Layer 3 of the OSI model. These devices use ARP to resolve IP addresses to MAC addresses on a local network.

ARP Usage Explained

ARP is crucial for communication within a local network. When a device wants to send data to another device on the same network, it needs to know the destination's MAC address. ARP helps in finding this MAC address based on the destination's IP address.

According to the reference:

ARP request is sent from a host (desktop), to learn the MAC address of a destination server after DNS has already resolved destination server IP address. It is only Layer 3 network devices (routers, Layer 3 switches, firewalls) and hosts that create ARP tables.

Devices that use ARP

The following devices use ARP:

  • Hosts: This includes devices like desktop computers, laptops, servers, and any other end-user device that communicates over a network. These devices initiate ARP requests to find the MAC addresses of other devices on the same network.
  • Routers: Routers use ARP to determine the MAC address of the next hop device in the network path.
  • Layer 3 Switches: These switches can perform routing functions and, therefore, use ARP to resolve IP addresses to MAC addresses within a VLAN or across different subnets.
  • Firewalls: Firewalls, especially those that perform routing, use ARP to communicate with devices on the network.

How ARP Works: An Example

  1. A host (e.g., a desktop computer) needs to send data to a server on the same network.
  2. The host knows the server's IP address (perhaps obtained through DNS).
  3. The host checks its ARP cache to see if it already knows the MAC address associated with the server's IP address.
  4. If the MAC address is not in the ARP cache, the host sends an ARP request. This is a broadcast message to all devices on the local network, asking, "Who has this IP address?"
  5. The server with the matching IP address responds with an ARP reply, containing its MAC address.
  6. The host updates its ARP cache with the IP address and MAC address of the server.
  7. The host can now send data directly to the server using the server's MAC address.

ARP Table

Hosts and Layer 3 devices maintain an ARP table (or ARP cache), which stores recently resolved IP-to-MAC address mappings. This table helps to avoid sending ARP requests for frequently contacted devices, improving network efficiency.

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