Which extensions to GRE tunneling provide session tracking and in-order packet delivery in exchange for...

D (GRE Key and Sequence Number extensions):The GRE Key field provides session identification for distinguishing between multiple GRE tunnels. The Sequence Number extension allows endpoints to track packet ordering and detect lost or out-of-order packets, enhancing reliability at the tunnel level if required.

Other options explained:

A: Protocol Type identifies payload type; Checksum detects errors but doesn't provide sequencing.

B: GRE Version and Reserved0 fields are not used for session or sequencing.

C: GRE does support optional extensions, contrary to this statement.