If you are experiencing issues connecting to Battle.net, common troubleshooting includes deleting the local cache folder or running the launcher as an administrator .
If you are seeing this term in an error log or encountering a connection issue related to it, you can try these standard fixes to reset your connection to Blizzard's data services: Network & DNS Reset bnet index server 2
Exploring BNet Index Server 2: A Deep Dive If you are experiencing issues connecting to Battle
The Index Server didn't know what happened inside your game of Starcraft. It didn't know you were rushing a Zerg base or dueling in the Blood Moor. It only knew that the door was open. Once you joined a game, the Index Server stepped away. The connection was purely between you and your opponent. It only knew that the door was open