What are you trying to do? I think you may be a little confused:
You forward ports from your router to an internal computer on the network so that those ports are available for use to that computer.
DNS is used to convert hostnames (like anandtech.com) into ip addresses. Many (most) routers come with their own DNS servers built in so that when they hand out DHCP leases they also handle DNS information. The client computer queries the router for instructions on how to resolve the hostname, and the router in turn queries the DNS servers that your ISP provides. There is more to the story, but it doesn't affect your set up.
Now, if you've assigned a static internal IP to one of the computers on your LAN so that you could forward ports to it for use by a particular application, then for DNS servers you can use the ones that your ISP provides for you, or you can use the ip address of your router.