Purpose: links the Network Layer (IP address) with the link layer (MAC address)

Case: A wants to send a datagram to B, but A doesn’t know B’s MAC address

  • A broadcasts an ARP query packet with an IP Address: “who has IP address”
  • B receives ARP request with that IP address on the LAN will respond with appropriate MAC address.
  • Generates an ARP Table maps IP to MAC
    • This is soft state, information that goes away unless refreshed. Each entry has a time limit

General Notes

  • Useful because frames use MAC addresses for addressing
  • ARP is stateless, doesn’t remember whether it sent a request (always reads response)
  • Not authenticated, anyone can ARP
  • Easily spoofed