REF: https://superuser.com/questions/932293/motorola-sbg6580-cable-modem-into-bridge-mode-on-bright-house-networks-does-not

Question being, with cable based connections where your incoming cable can split 3+ ways to TV, phones and an internet modem, do they relay on MAC addresses for routing and assigning IP information hence why you generally need to clone MAC Address?

Or am I wrong. Basically, Why and when is it required?

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3 Answers 3


The only reason to clone a MAC in this context, is because the ISP limits connectivity to that registered MAC. That would typically be the router supplied by the ISP -- you'd clone it's MAC onto the router of your choosing. Since the modem is the router these days (i.e. SBG6580), and few (if any?) ISPs still restrict connectivity to a "registered MAC", it's rarely done.

Personally, I do it to keep the same IP, and not have to reset the modem if I change routers. The modem does enforce a limited number of devices behind it -- (1) for most residential settings, (4) or more in business settings.


Generally you clone a MAC because you want the new device to look "the same" as the old one to an external authority.

Some providers require clients to register a MAC address before using it either explicitly through some kind of registration form or implicitly through some action. Examples of such impliicit registration include cable modems that will only accept the first MAC address they see after reset and wifi providers that use some kind of web based login form (technically the latter may use IP addresses to track users but due to the way DHCP is designed IPs tend to follow MACs).

Sometimes it is easier and/or cheaper to clone a MAC address than it is to get a registration changed.


Most, if not all, ISPs today, especially cable ones will provide service to a specific MAC address only. So if you decide to purchase your own gateway (e.g. modem+router+wifi) to avoid paying the ISP a monthly renting fee, you MUST call them and let them know that you have a new device with a new MAC.

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