In a home office environment with cable internet, can a hardware firewall be placed in front of/upstream from a cable modem to also protect the modem from tampering by the isp or a hacker?

3 Answers 3


Cable modems connect via coax cable to the ISP's network. I have not seen a hardware firewall that could connect in such a way. Besides which, the firewall would need to replicate the ISP's settings for the customer's site in order for traffic to be accepted.

In short: no.


No, you could replace your ISP-supplied device with your own if their systems and policies allow it, but there's nothing you could put in front that would protect an ISP supplied device.

You could put a firewall behind the ISP supplied device in order to protect your systems from the ISP supplied device if it was cracked, however that would not protect you from having your traffic sniffed by the ISP supplied device if it was taken over. If that is a concern your best bet is to use Tor or something like it.

  • TOR for an office environment?
    – Philipp
    Apr 13, 2014 at 23:05

If you deconstruct what a firewall before the modem would do, it becomes clear why it's not really practicable.

Data on almost all cable modems is carried over a coaxial cable system called DOCSIS. To manipulate the data carried on this system, you would need to convert the data from DOCSIS to a workable format to be screened by the firewall, then convert it back to DOCSIS format to feed into the cable modem.

In short, a cable firewall would include a modem, making a further one beyond it redundant. Some commercially available Cable modems actually include a customisable firewall, and many more will include some filtering rules that can't be changed.

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