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My linksy router worked fine with my old modem but then we got a new modem and it quit working I think it because the new modem give me the choice to have a public ip or a public ip and i don't know the difference????

GTB

I suspect the router's LAN configuration part is fine as it had worked in the past, unless the new ATT Modem is a modem / router using the same subnet as your Linksys provides.

First, make sure the ATT Modem performs properly by connecting a wired PC to the ATT modem's Internet feed. Reboot modem and pc first. If you can access the internet, all is working. However we need to know the pc's IP address (open command prompt by clicking on start, clicking on run - type in cmd and hit enter; at the > prompt in command prompt type in ipconfig and hit enter; write down the ip address, subnet mask, default gateway).

If you cannot access the Internet, contact ATT for assistance.

Now that Internet works, disconnect pc from modem, do not connect router to modem, connect router LAN port to pc via wired link. Turn on router and reboot pc. Use command prompt to determine your IP address with ipconfig command; write the ip address, subnet mask, default gateway down as well. Now if the first 3 sets of digits for ip address are the same when pc is connected to ATT modem and to Linksys router (e.g. 192.168.1.x for both, x can be different), we have a conflict which must be fixed or you will not get Internet. This change is called changing the subnet. You do this on the router; let's say both ATT modem and Linksys use 192.168.1.x subnet, 255.255.255.0 subnet mask; change Linksys' third digit to something else like 192.168.5.x. Save the change; you will have to reboot pc as well in this process; this must be done with a wired link to the Linksys LAN port. Once this is done and Linksys config saved, shut down pc, Linksys, and ATT modem for at least 0.5 min and then turn them back on. All should work with wired link to the Linksys. After this, the wireless should also work.