One can't swap cable modems like that. The ISP must be in the loop and change their system to allow the new modem. If you happen to give them the wrong MAC number what you wrote will happen.
Why I must read the right words is simple. A few folk want to change the modem but don't want to tell the carrier or ISP.
Having recently purchased an Arris Surfboard SBG6580 cable modem router, I securely connected a coax cable leading from a wall into the back of the unit. The unit was then powered on, which led to a number of front-panel lights to flash and then stablise with a solid colour.
Here's the squence of colours and statues:
1. The power light, download light, upload light, globe light, and wifi light all flash.
2. The power light, and wifi light both stablise in a solid colour. The download light remains flashing, and doesn't stablise.
I've contacted Xfinity support a number of times, and they (and I) have performed a number of resets both remotely and at the mains.
What it comes down to is they ISP/Comcast are unable to see the cable modem router (i.e. it appears offline to them) - but I can assure you and them that it is very much switched on.
Can anyone offer advice on what the issue might be? A switched on, coax-cable connected modem that appears offline to the ISP?
Thanks in advance.