MAC Cloning

Some ISPs require you to "clone your MAC address" if you install a router between your NIC and your cable modem. Apparently, your ISP knows your machine's MAC address and will only allow the cable modem to communicate w/ it. Therefore, if you have a router between them, it will not talk to the NIC.
Basically, you have to tell the router to lie to the cable modem as if it were your computer.

Anyway, my question is this: I read that MAC addresses are not broadcasted, so how does the ISP know my MAC address? Is it really the cable modem that "knows" my MAC?

-Sorry if this is beyond the scope of the Network+ exam, but I can't find a better forum to post it in.

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Comments

2lazybutsmart

Any machine on the same broadcast domain as your computer will eventually know it's MAC address (if it needs to). MAC's are resolved through ARP. They're not broadcasted to the public unless there's an RARP in progress.

I think the ISP would know the MAC address you're using is if they gave you the hardware in the first place. Another way they would know your MAC address is if you're on a live link with their network. Eventually, all data frames to your computer/router/switch must be resolved at their side, and they're switch/router will add your MAC address in it's database for use in the future.