D-Link DGS-3700 user manual Ethernet Gratuitous ARP

DGS-3700-12/DGS-3700-12G Series Layer 2 Gigabit Ethernet Switch User Manual

Ethernet

Gratuitous ARP

Destination	Source
address	address
(6-byte)	(6-byte)

FF-FF-FF-FF-FF-FF 00-20-5C-01-11-11

Ethernet	H/W type	Protocol	H/W	Protocol	Operation
type		type	address	address
			length	length
(2-byte)	(2-byte)	(2-byte)	(1-byte)	(1-byte)	(2-byte)
806					ARP reply

Sender H/W	Sender	Target H/W	Target
address	protocol	address	protocol
	address		address
(6-byte)	(4-byte)	(6-byte)	(4-byte)
00-20-5C-01-11-11	10.10.10.254	00-20-5C-01-11-11	10.10.10.254

Table-5

A common DoS attack today can be done by associating a nonexistent or specified MAC address to the IP address of the network’s default gateway. The malicious attacker only needs to broadcast ONE Gratuitous ARP to the network claiming it is the gateway so that the whole network operation will be turned down as all packets to the Internet will be directed to the wrong node.

Likewise, the attacker can either choose to forward the traffic to the actual default gateway (passive sniffing) or modify the data before forwarding it (man-in-the-middle attack). The hacker cheats the victim’s PC to think that it is a router and cheats the router to think it is the victim. As can be seen in Figure-5 all traffic will be then sniffed by the hacker but the users will not notice anything happening.

Figure-5

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