Source:
here In 2005/2006 both Dir en Grey and Kagerou performed at the festival, now Dir en Grey are listed as one of the bands performing there this year.
For those of you who don't know what Rock am Ring/Rock im Ring is here's a brief description about the german festival,
"The Rock am Ring (Rock at the Ring) and Rock im Park (Rock in the Park) festivals are two simultaneous rock music festivals held annually in Germany. While Rock am Ring takes place at the Nürburgring racetrack in the west of Germany, Rock im Park takes place in and around the Frankenstadion in Nürnberg, in the south east of Germany.
Both festivals are usually regarded as one event with a mostly identical lineup for both festivals. All artists perform one day at Nürburgring and another day at Nürnberg during the three day event. There have been minor exceptions in the past years where an artist will be announced for one of the festivals only.
Together Rock im Park and Rock am Ring are the largest music festivals in Germany and one of the largest in the world with a combined attendance of just over 150,000 people in 2007, selling out both events in advance for the first time"