D-Link DES-3550 Product Manual - Page 283

xStack® DES-3500 Series Layer 2 Stackable Fast Ethernet Managed Switch User Manual How ARP spoofing attacks a network ARP spoofing, also known as ARP poisoning, is a method to attack an Ethernet network which may allow an attacker to sniff data frames on a LAN, modify the traffic, or stop the traffic altogether (known as a Denial of Service - DoS attack). The principle of ARP spoofing is to send the fake, or spoofed ARP messages to an Ethernet network. Generally, the aim is to associate the attacker's or random MAC address with the IP address of another node (such as the default gateway). Any traffic meant for that IP address would be mistakenly re-directed to the node specified by the attacker. IP spoofing attack is caused by Gratuitous ARP that occurs when a host sends an ARP request to resolve its own IP address. Figure-4 shows a hacker within a LAN to initiate ARP spoofing attack. Figure-4 In the Gratuitous ARP packet, the "Sender protocol address" and "Target protocol address" are filled with the same source IP address. The "Sender H/W Address" and "Target H/W address" are filled with the same source MAC address. The destination MAC address is the Ethernet broadcast address (FF-FF-FF-FF-FF-FF). All nodes within the network will immediately update their own ARP table in accordance with the sender's MAC and IP address. The format of Gratuitous ARP is shown in Table-5. 268