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ARP and its types
ARP (Address Resolution Protocol) is a communication protocol used to map a network address, such as an IP address, to a physical address, such as a MAC address. It is an essential component of the TCP/IP protocol suite, and it allows devices on a local area network (LAN) to communicate with each other. In this article, we will explore the different types of ARP, their uses, and examples of how they are implemented in a network.
Introduction to ARP
ARP is a simple protocol that operates at the Data Link Layer (Layer 2) of the OSI model. It is responsible for resolving IP addresses to MAC addresses. This is necessary because IP addresses are assigned to devices on a network, but the data link layer uses MAC addresses to identify devices. When a device wants to send a packet to another device on the same LAN, it uses ARP to determine the MAC address of the destination device.
When a device wants to send a packet to another device on the same LAN, it broadcasts an ARP request packet to all devices on the network. The packet contains the IP address of the destination device. The device with the matching IP address responds with its MAC address, and the sender can then use this information to send the packet to the destination device.
Types of ARP
ARP Request
ARP requests are used to determine the MAC address of a device on a LAN. When a device wants to send a packet to another device, it broadcasts an ARP request packet containing the IP address of the destination device. The device with the matching IP address responds with its MAC address, and the sender can use this information to send the packet to the destination device.
Example − A device on a LAN wants to send a packet to another device with the IP address 192.168.1.100. It broadcasts an ARP request packet containing the IP address 192.168.1.100. The device with the IP address 192.168.1.100 responds with its MAC address, 00-11-22-33-44-55. The sender can now use this information to send the packet to the destination device.
ARP Reply
ARP replies are used to respond to ARP requests. When a device receives an ARP request packet containing its IP address, it responds with its MAC address. This allows the sender to send packets to the destination device.
Example: A device on a LAN receives an ARP request packet containing the IP address 192.168.1.100. It responds with its MAC address, 00-11-22-33-44-55. The sender can now use this information to send packets to the destination device.
ARP Cache
ARP cache is used to store recently resolved IP-MAC address mappings. When a device sends an ARP request, it stores the mapping in its ARP cache. This allows the device to quickly send packets to the same destination device without having to send an ARP request again.
Example − A device on a LAN sends an ARP request to determine the MAC address of the device with IP address 192.168.1.100. It receives a response with the MAC address 00-11-22-33-44-55. The device stores this mapping in its ARP cache. When it wants to send a packet to the same device again, it can quickly retrieve the MAC address from its ARP cache instead of sending another ARP request.
ARP Poisoning
ARP poisoning is a type of attack in which an attacker sends false ARP replies to a device, causing it to update its ARP cache with incorrect information. This can to intercept traffic intended for another device, or even redirect traffic to the attacker's device.
Example - An attacker sends false ARP replies to a device on a LAN, claiming that the attacker's device has the IP address 192.168.1.100 and the MAC address 00-11-22-33-44-55. The device updates its ARP cache with this information and sends packets intended for the device with IP address 192.168.1.100 to the attacker's device. The attacker can then intercept or redirect these packets.
Preventing ARP Poisoning
To prevent ARP poisoning, there are several techniques that can be used −
ARP Inspection − ARP inspection is a technique used to validate ARP requests and replies. It compares the ARP packets to a pre-configured list of allowed IP-MAC address mappings and discards any packets that do not match.
Port Security − Port security is a technique used to limit the number of MAC addresses that can be learned on a switch port. This can prevent an attacker from flooding the switch with false ARP replies.
ARP Spoofing Detection − ARP spoofing detection is a technique used to detect and alert on ARP spoofing attempts. This can be done by monitoring the ARP cache for changes, or by using a protocol analyzer to capture and analyze ARP packets.
Virtual Private LAN Service (VPLS) − VPLS is a technique used to segment a LAN into multiple virtual LANs. This can prevent an attacker from broadcasting false ARP replies to the entire LAN.
Conclusion
ARP is a critical protocol that plays a vital role in allowing devices on a LAN to communicate with each other. However, it is also vulnerable to attack, and it is important to understand the different types of ARP, their uses, and how to protect against ARP poisoning. By implementing techniques such as ARP inspection, port security, ARP spoofing detection, and VPLS, network administrators can ensure the integrity and security of their LANs.
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