Read up on "split DNS"
Add a static DNS entry on your router for the LAN IP address for your webserver.
Of course you'll be otherwise landing on the interface page of your router when the router's WAN IP address is resolved as your webserver.
My previous router was a Linksys WRT320N
how does that compare to the model of CRS you have?Number of Antennas 3
RF Pwr (EIRP) in dBm 17 dBm
Antenna Gain in dBi Main Antenna*: 1.5 dBi
Third Antenna: 2.2 dBi