I got a new Comcast wireless modem/router combo because they told me my old modem might not work with some changes they were making to their network. I had my old Comcast modem connected to a Cisco valet wireless router and everything connected and worked great. I should have left well enough alone. Unfortunately the new Comcast wireless modem/router combo doesn't seem to work with my old Cisco Valet wireless router. I read that since the new modem has wireless capability, the wireless signals from the new modem and the old router may be conflicting. The wireless on the new Comcast modem/router DOES finally work with all of my devices after lots of finagling, but I would like to have my old Cisco wireless router work with the new wireless modem/router from Comcast. The Comcast router doesn't seem to be quite as fast and seems to disconnect at times.
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call Comcast and have them help you to configure the new modem/router into bridge mode so it works like a modem only and then connect your router to it.
another reason the old router does not work could be that both the new modem/router and old router use the same IP scheme. Meaning if the WAN side and the LAN side of your old router both are on the 192.168.1.xxx scheme your router does not know how to direct traffic.
Unfortunately Comcast is absolutely useless. I will never call them again for help. I know more than most of the people at Comcast I worked with today, and that's not saying much. I spent three hours on chats and the phone with four different people at Comcast. Initially I could only connect my laptop to the new Comcast router modem combo but my iPhone etc wouldn't connect. (I had given up on getting my old router to work with the new modem router combo but needed all my devices to be able to connect wirelessly to the new modem router combo. ) By the time I was done with them I couldn't connect anything to the new modem router combo, so was actually worse off than when I started.
With some troubleshooting on my own, i managed to get all of my devices connected wirelessly to the new Comcast modem router combo. What the Comcast instructions didn't say is that if you change the wifi password key they give you----which I had done on my laptop, as the instructions suggested-----the new password will only work on the device on which you changed the password! For each device you want to connect wirelessly to the modem router combo, you must either use the password key supplied with the modem router combo, or change the password for each device. I figured since I changed the modem router combo's password on my laptop, then this new password would work for all of my devices, but it only worked on my laptop. Not one of the Comcast support people thought about this or knew of it.
I managed to get things working on my own so I'm connected to the Comcast wireless modem router combo now, and everything at least works but would like to use my old router and use the Comcast wireless modem router combo ONLY AS A MODEM. BUT won't ask Comcast for help again.
If anyone could tell me how to configure the Comcast wireless modem router combo as a modem only that would be wonderful. Or maybe I should just leave well enough alone :-)