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Does anyone have an idea of how many IP addresses max a DOCSIS 3 cable modem can support? I seem to get varying answers even from different people at our ISP.

Thanks, Ryan

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up vote 2 down vote accepted

I'm assuming you mean the number of public addresses that may be either assigned to the modem or routed?

To my understanding, DOCSIS is Layer 2 and below. It shouldn't impose any limitation on assigned IP addresses at all. In the same way, using coax or twisted-pair ethernet, or TokenRing, wouldn't impose a limit on the number of IP addresses on a given port of a device. Hell, you might not even be running IP on a given physical layer, or multiple protocols like IP + IPX + NetBEUI.

Your specific modem may have certain limitations, but without knowing the model, we can't tell you. Your cableco may also have imposed a limit.

Now, if you're referring to a maximum number of internal private-IP addresses that may be NAT-ed, that depends strictly on the router's config, including CPU and RAM, and any provider-imposed limitations as well.

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Thanks for the info. The cable modem is an Arris WBM760A (DOCSIS 3). – rmwetmore Oct 25 '10 at 15:51
Also, we are just using it as a bridge. I don't think it has routing capability. – rmwetmore Oct 25 '10 at 15:53
If you know that you're strictly using it as a bridge, then the answer is "no limitation." A bridge is a layer-2 device. An ethernet hub can't limit the number of IP addresses on the devices attached to it, right? Seems like the same scenario. – mfinni Oct 25 '10 at 16:22

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