What is the purpose of the ServerIndex property in the expanded node id

This article is relevant for all .Net products

The ServerIndex is an advanced field that provides the information if the addressed NodeID is located on the local Server, or it resides on a remote Server. This is relevant for the Servers that act as aggregation Servers and retrieve their data from underlying OPC Servers. Therefore there is the ServerIndex that identifies the Server that contains the TargetNode. This Server may be the local Server or a remote Server.

This index is the index of that Server in the local Server's Server table.
The index of the local Server in the Server table is always 0.
All remote Servers have indexes greater than 0.

The Server table is contained in the Server Object in the AddressSpace. The Client may read the Server table Variable to access the description of the target Server.

Using a normal non aggregation Server / Server chaining solution that parameter is always 0.