Address Resolution Protocol (Arp)

IP addresses are used by computers to identify each other on a network, while MAC addresses are physical identifiers assigned to network cards.

Purpose of ARP

• To resolve IP addresses to MAC addresses. When a device sends a packet to another device on the same network, it needs to know the MAC address of the destination device in order to deliver the packet.
• To maintain a cache of IP-to-MAC address mappings. This cache can be used to reduce the number of ARP requests that need to be sent, which can improve network performance.

How ARP Works

1. Device sends an ARP request. The device broadcasts an ARP request message to the network, asking "Who has the IP address of [destination IP address]?"
2. Device that owns the destination IP address sends an ARP reply. The device that owns the destination IP address responds with an ARP reply message, including the destination device's MAC address.
3. Device caches the MAC address. The device that sent the ARP request caches the MAC address of the destination device for future use.

ARP Poisoning

ARP poisoning is a type of attack that can be used to redirect traffic to an attacker-controlled device. The attacker sends forged ARP replies to the network, claiming to be the gateway or other trusted device. This can cause devices to send traffic to the attacker's device instead of the intended destination.

Virtual Router Density Protocol (VRRP)

VRRP is a protocol used to provide fault tolerance for virtual routers in a network. It allows multiple devices to share the same virtual IP address, and automatically takes over for the active device if it fails.

ARP in Load Balancing

ARP can be used to implement load balancing for servers in a network. By distributing the MAC addresses of the servers over multiple devices, traffic can be evenly distributed among the servers.

Summary

ARP is a critical protocol for network communication. It allows devices to resolve IP addresses to MAC addresses, which is necessary for sending and receiving packets. While ARP can be used for malicious purposes, it is an essential part of a well-functioning network.