blinking red ethernet light

[Erin77]

Just activated new xfinity internet service with brand new CM500 modem- all lights are solid green except for the Ethernet light, which is blinking red. Xfinity customer service says my modem is active and working perfectly on their end. Can’t access internet with Ethernet cord plugged directly into my computer or plugged into my router. Switched Ethernet cords to see if that was the problem and no change. 😞 please help me!

[schumaku]

As per the CM500 User Manual p.6 there is no red LED on the Ethernet port:

An amber LED does indicate there is a 10 or 100 Mbit/s link speed negotiated between the computer. This can be a limitation of the computer Ethernet interface, or a bad/incomplete cable - a Gigabit Ethernet link requires four correctly wired and patched pairs. This should allow communication between the computer and at least the Cable Modem on http://192.168.100.1/ - permitting the computer is set-up to DHCP (and getting a public IP from the ISP DHCP).

[schumaku]

Is your Internet service activiated -How do I activate my Internet service with Comcast XFINITY?

[Erin77]

Yes, the internet service is activated.

[Erin77]

Okay, the amber light is still blinking, but now when I plug the Ethernet cord directly into my computer, the internet works on my computer just fine. When I plug into the router though, I can’t connect to the WiFi. My router (an apple airport express) has a solid green light and worked just fine a couple days ago with my old modem, so I don’t think my router is the issue. My devices recognize my network and try to connect, but cannot.

[schumaku]

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@Erin77 wrote:
Okay, the amber light is still blinking, ... My router (an apple airport express)...

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Airport Express routers are supporting 10/100 Mbit/s only, so the amber LED is OK.

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@Erin77 wrote:
  but now when I plug the Ethernet cord directly into my computer, the internet works on my computer just fine. When I plug into the router though, I can’t connect to the WiFi.

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Wait. Your ISP will only allow one MAC address on the cable modem. If you had connected the computer before direct to the CM500 (e.g. to "activate the Internet") it won't issue a public IP address to your router WAN port. Power-off the router, reboot the CM500, wait some minutes, then power-up the router again.

The can't connect to the  WiFi is a little bit vague - I would assume the router does come up anyway, and the wireless connection can be established, regardless if the router "has Internet" or not. However, some operating systems make users believe that if these systems can't reach the Internet, that the Wireless connection can't be established.

[Erin77]

I powered down, rebooted, powered back up, and no change.