The intended purpose of this feature is to introduce a server streaming RPC. When a client subscribes to this RPC, they will receive a message anytime there is an update to the hardware programming state of an MPLS route or the Nexthop-Group to which it points to. Note that messages will only be streamed in this RPC callback for versioned MPLS routes that point to versioned nexthop-groups. Messages will not be streamed via this RPC for MPLS routes and Nexthop-Groups that don’t meet this criteria.