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DGS-3120 Series Managed Switch CLI Reference Guide 
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Table 3 ARP Payload 
 
When PC B replies to the query, the “Destination Address” in the Ethernet frame will be changed 
to PC A’s MAC address. The “Source Address” will be changed to PC B’s MAC address (see 
Table 4).  
 
 
Table 4 Ethernet Frame Format 
 
The switch will also examine the “Source Address” of the Ethernet frame and find that the address 
is not in the Forwarding Table. The switch will learn PC B’s MAC and update its Forwarding Table. 
 
 
 
How ARP Spoofing Attacks a Network