Techniques are described for generating a No-Acknowledgement (NACK) message if the installation of a route for a label-switched path at a router has failed or is likely to fail. In some examples, a network device includes at least one processor and at least one module operable by the at least one processor to: receive a request to forward network packets for an LSP; responsive to receiving the request, initiate configuration of at least one forwarding unit of the network device to forward network packets for the LSP; generate a NACK message that indicates the at least one forwarding unit is not configured to forward the network packets for the LSP; and terminate based at least in part on the NACK message, the configuration of the at least one forwarding unit for the LSP.