RSVPTE

RSVP-TE, or RSVP Traffic Engineering, is an extension of the Resource Reservation Protocol that enables signaling and reservation of network resources to establish MPLS Traffic Engineering label-switched paths (LSPs). It was developed to support explicit routing and bandwidth guarantees in IP/MPLS networks, allowing operators to steer traffic along routes chosen for performance and efficiency rather than simple hop-by-hop forwarding.

RSVP-TE uses Path and Resv messages. Path messages travel toward the destination and carry an Explicit Route Object (ERO) to specify the intended route (either strict or loose). Resv messages return toward the source and carry a Reservation Style (such as fixed-filter or shared) and a bandwidth reservation, thereby reserving the required resources along the path. The signaling relies on IGP-based TE extensions, such as OSPF-TE or IS-IS-TE, to advertise per-link bandwidth and metrics, which are used by CSPF to compute an acceptable path.

RSVP-TE LSPs are typically unicast, but multipoint LSPs are supported. The protocol also enables fast failure protection and restoration through preconfigured backup LSPs and rapid rerouting. Administrators can create primary and secondary LSPs, enabling protection against link or node failures.

RSVP-TE has become a foundational technology for MPLS networks requiring traffic engineering. It is specified in RFC 3209 and has undergone several updates and extensions. As networks evolve towards segment routing, RSVP-TE remains widely deployed in legacy MPLS deployments and coexists with newer architectures.