In one example, a backup intrusion detection and prevention (IDP) device includes one or more network interfaces to receive a state update message from a primary IDP device, wherein the state update message indicates a network session being inspected by the primary IDP device and an identified application-layer protocol for the device, to receive an indication that the primary device has switched over or failed over to the backup device, and to receive a plurality of packets of the network session after receiving the indication, each of the plurality of packets comprising a respective payload including application-layer data, a protocol decoder to detect a beginning of a new transaction from the application-layer data of one of the plurality of packets, and a control unit to statefully process only the application-layer data of the network session that include and follow the beginning of the new transaction.