How does the MAC work?

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A+ Dec 8, 2000

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A MAC address is a 48-bit address represented by six pairs of hexidecimal values. The MAC address, which is assigned by the manufacturer of the network card before it is shipped to be sold, is designed to be unique and is used to help identify a single machine on a network.

http://www.webopedia.com/TERM/M/MAC_address.html

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The MAC address does everything. On a network, machines don't really talk by IP address, they actually talk by MAC address. Just as there is DNS to convert between hostnames and IPs, there is ARP to convert between IPs and MAC addresses.


It works like this, roughly:
1. You want to get to www.yahoo.com.
2. DNS converts www.yahoo.com to IP.
3. Yahoo's IP isn't on your local network, so you have to talk to your router to pass your packets on.
4. You know your router's IP(its loaded as part of your network settings), but need its MAC address (if its not in the ARP cache) to actually talk to it.
5. A Broadcast(MAC address of FF:FF:FF:FF:FF:FF) is sent to all machines on your local subnet, looking for machine with your router's IP.
6. You router responds with its MAC address.
7. You machine puts it in its ARP cache, and communicates with it from now on.
8. Steps 3-7 occur at every step of the route.

Hope thats not too confusing.

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