All issues have been resolved by the affected DNS provider, and DNS replication should be completed. At this time I'm going to lock this thread to prevent bumping, if you continue to experience issues please [Contact Support](http://support.leagueoflegends.com) for further assistance and individual troubleshooting.
Update: The majority of DNS providers are now returning correct responses - most players should be able to log in now. There may be a few still receiving errors, but these should clear up of their own accord once they receive updates. We'll be continuing to monitor.
Update: We are beginning to see signs of recovery. We are continuing to monitor, as we're not seeing global resolution yet, we're continuing to monitor and work with the affected external DNS provider for further information.
We are currently experiencing issues resolving to l3cdn.riotgames.com, resulting in RADS errors for a number of players. At this time please hold off on troubleshooting from your end, as we are aware and investigating.
I'll update this once I have further information, but I wanted to post ASAP to avoid people following normal troubleshooting steps as they won't work in this instance.