External wifi router can't to get internet through cable modem, but can when passed through another router
My current wifi setup is an Orbi RBR10 wifi router connected via ethernet cord to an ancient Apple AirPort Time Capsule, which in turn is connected via an ethernet cord to an old Cisco DPO3212 (or maybe DPQ3212) cable modem. This setup is working fine, but the Time Capsule locks up often and has to be rebooted to get the wifi working again.
I want to remove the Time Capsule from the chain, but if I plug the Orbi router directly into the cable modem the wifi network no longer has an internet connection. It doesn't matter which ethernet cable I use to make the connection. All the articles I can find just imply that I should be able to plug the Orbi into the cable modem and it should work. I've tried rebooting everything after switching the connections.
Does anyone have an idea what might be going on? Does this sound like a problem that can be fixed through technical support on the Cox side or the Orbi side?
Reading what you've posted, it sounds like a simple case of the modem was not rebooted when connecting it to a different Ethernet device. The modem will only provide a connection to whatever device was connected to the Ethernet port when it last booted up. If you connect a different PC/router/etc., rebooting your modem should make it work again.
To add to my above post, if you're DPQ3212 has the battery backup installed (which as old as they are you may have actually gotten a battery backup with it), that'll also need to be pulled during a power cycle otherwise the modem won't actually lose power when the power cord is removed.