I finally had Comcast put the Arris modem/router into bridge mode. The guy at Comcast phone support admitted he chose to do the same thing to his at home. (This supports all the comments about this modem/router being crap.) I have now installed my old Netgear router successfully. Network has now been operating properly for about 24 hours. Assume all is well unless I inform otherwise. I begged for Comcast do to this months ago, right after I received the new modem (handles higher speeds). They were clueless! I was clueless as well about the bridge mode...until I read the posts here. THANK YOU for all who contributed.