This entry continues where Sniffing Networks Part 1 left off. If you didn’t read it, as long as you understand how switches work and why we have MAC addresses, you’ll be able to understand this entry. The physical wire may talk in MAC addresses, but when’s the last time you typed a MAC address into a browser location bar? (You haven’t, except by accident, and certainly not expecting to get anywhere with it.) Computers talk in IP addresses, not MAC addresses, so how does the switch know what port to send the packet on to if it’s only given the IP address? Address Resolution Protocol, or ARP. ARP is another table that lives in each router (and computer) to map[…]