Docsis gives the ISP the ability to control the router, but they are very bad at it and even if they aren't it's often the manufacturers who are the problem. So I always have bought my own cable modems instead of renting from the ISP. The last time I did this I went with a good Motorola, but come to find out arris has bought them out, I did some scans, notice it's vulnerable and needs and update, so I go to the arris website. Can't find the update anywhere. End up calling them and get told, even though I own the equipment, they only release updates to ISPs or "partners" and no I can't have it! Wtf!?
Docsis, even 3, is a shitty spec that needs to die.
So really the best thing you can do and what I suggest to people is to put the cable modem in bridge/passthrough mode after checking all settings, and then hit your own router.
Except most people, as the article states, just go get some crappy linksys (cisco owned), netgear, Asus, belkin, etc, which have their own set of problems. It's better with openwrt/ddwrt/tomato but there is a better way.
My favorite setup is thus:
ISP Router in passthrough
Ubiquiti edgerouter
Ubiquiti APs