>>
>>UPDATE. The problem was with xFinity modem. I reset it and all works now.
>
>rebooting is better most of the time. If you have not checked for firmware updates, after fresh reboot (best done disconnected) is a good time to enter the router software, reconnect router to the net and check for updates.
>There HAVE been some problems fixed recently in some router models.

Now THAT opens a can of worms. Routers are computers (often Linux-based), and like any other computer, should be periodically updated. Many residential/consumer routers quickly go out of support; many are never updated throughout their service lives. That makes them juicy targets.