I have seen a dozen threads of comcast issue, but my problem is unique that it totally make no sense to me. The advanture starts when I was trying to replace Linksys with N300.
1. I don't think comcast has binding MAC address, at least my laptop and old Linksys router uses different MAC address, they both connect with modem. I even tried clone MAC into buffalo: no help as expected.
2. N300 is able to get WAN IP address from cable modem through DHCP. I can see the wan ip from the admin page. Laptop can ping the WAN IP (e.g. 78.111.111.128), but ping to the WAP gateway (e.g. 78.111.111.1) fails.
3. From my laptop (and other devices), browser connection timeout, ping packets droped 100%, but DNS lookup works: aka my laptop can dns resolve any domain name through N300 router, weird! right? It couldn't be my laptop issue, I tried couple devices and with wireless and wired. All these devices work with my old linksys.
4. From N300 admin page, I can ping/traceroute any places and run "wget" to pull down web pages. If you don't know what I am talking about: go to administrator -> command line tool, type unix command like ping, traceroute, it WORKS, is that weird?
so this means the WAN is in fact working properly, but the router is blocking every internet connection from LAN.
5. I have updated DDRT firmware in admin page to latest version 19152 even I have no access to internet from laptop to external world. Isn't that absolutely ridiculous?
6.please don't let me to recycle the modem, router in a subsequent way, I have done all of these steps dozens of times. Router switch is on, movie mode is off. I also factory reset (firmware won't be reset though) few times.