This identifies which specific tunnel within the decap group is currently active for receiving and unwrapping incoming traffic, letting the admin detect when the decap side of a protected service has switched to its backup path. Since encap and decap directions can fail independently (e.g., a unidirectional fiber cut), tracking this index separately from the encap active index is necessary to fully understand which direction of the service switched over. A change in this value alongside an unchanged encap active index would point to an asymmetric, receive-side-only failure.