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 130.207.160.47?”
- 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