I was supplied a Cisco DPC3825 modem by my ISP and use a Cisco E4200 as my main router.
Today the Internet just stopped working, just out of the blue, I can't think of anything that would have triggered it. It's been working pretty good for the past month except for a few random blips here and there.
After some trouble shooting I realized that a direct wired connection to the modem would get me Internet access but if I was wired to the router as I was before I would have no connection. Assuming it was router I connected a TP-Link WR841N but it had the exact same problem. Also, connecting to the router via Wi-Fi from multiple devices will connect me to the router but I still can't get access to the Internet. From these test, it seems that the modem just won't send Internet through to the router but is clearly connecting and able to directly connect to my PC.
What I've Tried
- A full reset and factory reset on the E4200
- A full reset on the modem (but I believe my ISP has remote access to the modem because
the passwords and so on are always set back). - My ISP has remotely reconfigured the modem
What I Should Try
What else can I try? What should I do to try to narrow down the issue? Can you figure out what the problem might be based on this information?
My set up is 3825 purely as modem. My ISP put it in "Bridge Mode". Connected via port 1 to the "Internet" (WAN) port on the 4200, which was my router handling wired and wireless connections.
Best Answer
See my comment for the information needed to do more than guess. But given just the information you've given us, my guess is that the problem is that you have two DHCP servers on your network. Machines connected to the E4200 wireless router tend to get assigned DHCP addresses from the E4200 since it responds fastest, leaving them with no Internet access because the DPC3825 is the router managing your Internet connection.
If my guess is right, the fix is simply to disable the DHCP server in the E4200.
It could be worse. The two routers could have the same LAN IP address. That obviously won't work.
Note that having two routers in the same LAN is a fairly advanced configuration and requires network planning and some understanding of networking to properly configure and maintain. It's complex enough that if you have no idea how it's supposed to work, it's not going to work. Default configurations only "just work" in the simple configurations they are made for.