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DGS-3400 Series Layer 2 Gigabit Ethernet Managed Sw itch
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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 itself. The “Sender H/W Address” and “Target H/W address” are filled with the same source MAC address itself. 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 the
following table
.
Table 5
Destination
Address
Source
Address
Ethernet
Type
H/W Type Protocol
Type
H/W
Address
Length
Protocol
Address
Length
Operation
Sender H/W
Address
Sender
Protocol
Address
Target H/W
Address
Target
Protocol
Address
(6-byte)
(6-byte)
(2-byte)
(2-byte)
(2-byte)
(1-byte) (1-byte)
(2-byte)
(6-byte)
(4-byte)
(6-byte)
(4-byte)
FF-FF-FF-FF-FF-FF
00-20-5C-01-11-11
0806
ARP relay
00-20-5C-01-11-11
10.10.10.254 00-20-5C-01-11-11
10.10.10.254
Port1 00-20-5C-01-11-11
Port2 00-20-5C-01-22-22
Forwarding Table
Ethernet Header
Gratuitous ARP
