The Domain Name System is supposed to translate the domain names into numerical IP addresses. The trouble is, your internet provider may not have the fastest or most reliable DNS servers available. You can easily configure your Wi-Fi connections in iOS to use better DNS servers, like those run by Google or OpenDNS. Here’s how to get it done.
Go to your settings app and tap Wi-Fi settings.
On the Wi-Fi screen, tap the information button next to the network you want to configure.
On the information screen for the Wi-Fi network you chose, you’ll see the automatically assigned IP addresses for the DNS servers listed in the “DNS” box. Tap that box and use the keyboard to delete all the information that’s there. Don’t worry about writing it down anywhere; it’s easy to get back if you need to.
In the now blank DNS box, type the IP address for the primary and secondary DNS servers you want to use. Separate the two IP addresses with a comma.
For what DNS servers are used for depends on your internet connection. Favorites include Google Public DNS (18.104.22.168 and 22.214.171.124) and OpenDNS (126.96.36.199 and 188.8.131.52), but there are others. If you are running Windows or Linux you can use a tool called Namebench which will test your connection against different DNS providers–including Google and OpenDNS–and show you how much faster different options are than your current DNS servers.
And that’s about it. The new DNS servers you set up will stay in place even when your router or ISP refreshes the IP address lease. If you ever have iOS forget the network, though, it will revert to the automatically assigned DNS servers. At that point, you’ll need to enter your own server addresses again if you want. And if you want to change back to the automatically configured DNS servers without forgetting the network first, just return to that settings page and delete everything in the DNS box, iOS will grab the right DNS servers for you.