What is ARP protocol?

ARP is a protocol used to resolve IP addresses to physical machine addresses, also known as Media Access Control (MAC) addresses. ARP is used to determine the MAC address of a device on a network, given its IP address.

How Does ARP Work?

1. ARP Request: A device on a network sends an ARP request packet to the broadcast address (FF:FF:FF:FF:FF:FF), asking for the MAC address of a specific IP address.

2. ARP Reply: The device with the requested IP address responds with an ARP reply packet, containing its MAC address.

3. ARP Cache: The requesting device stores the MAC address in its ARP cache, so it can quickly reference it for future communications.

Types of ARP Messages:

1. ARP Request: Sent by a device to request the MAC address of a specific IP address.

2. ARP Reply: Sent by a device in response to an ARP request, containing its MAC address.

ARP Table:

An ARP table, also known as an ARP cache, is a table stored on a device that maps IP addresses to MAC addresses. The ARP table is used to:

1. Speed up communications: By storing the MAC addresses of frequently accessed devices, a device can quickly reference the ARP table instead of sending an ARP request.

2. Reduce network traffic: By storing the MAC addresses of devices on the network, a device can avoid sending ARP requests for devices it has already communicated with.

ARP Spoofing:

ARP spoofing is a type of cyber attack where an attacker sends fake ARP messages to a network, associating their MAC address with the IP address of a legitimate device. This can allow the attacker to:

1. Intercept traffic: By associating their MAC address with the IP address of a legitimate device, an attacker can intercept traffic intended for the legitimate device.

2. Launch man-in-the-middle attacks: An attacker can use ARP spoofing to launch man-in-the-middle attacks, where they intercept and modify traffic between two devices.

Preventing ARP Spoofing:

To prevent ARP spoofing, you can:

1. Use static ARP entries: Configure static ARP entries on devices to ensure that the MAC address associated with an IP address is correct.

2. Implement ARP inspection: Use ARP inspection tools to monitor ARP traffic and detect potential ARP spoofing attacks.

3. Use secure networking protocols: Use secure networking protocols, such as HTTPS and SSH, to encrypt traffic and prevent eavesdropping.