I recently had an issue with a Netgear R7000P router.
It would not go to a specific website but would go to any other site ok.
It would no go to http://iaai.com
After 4 days, 180 miles, and 6 support agents I got a good one with number 7.
We tried many possible solutions including resetting the router, changing the DNS servers and on and on.....
The computer would access the site if plugged directly to the ISP, but not if ran through the R70000P router.
Also the computer would access the site if I used a VPN on the computer through the router.
Clearly the router was not letting the website through.
The solution was to log into the router:
Under Advanced > Setup > WAN Setup, He had me put a check mark on the NAT Filtering item Disable SIP ALG and change it to Open.
I hope this helps others with this issue.