xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch CLI Manual
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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. 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.
Port 1
Port 23
Port 2
Port 24
A
IP: 10.10.10.1
MAC: 00-20-5C-01-11-11
IP: 10.10.10.3
Router
B
DNS server
IP: 10.10.10.253
MAC: 00-20-5C-01-53-53
IP: 10.10.10.2
MAC: 00-20-5C-01-22-22
A wrong ARP entry spreads over
the network to spoof all PCs
Internet
MAC: 00-20-5C-01-33-33
Hacker
IP: 10.10.10.254
C
Port 3
MAC: 00-20-5C-01-54-54