A service provider network is currently divided into five IGP domains; four IS-IS domains and one OSPFv2 domain. Because of customer demand, it has been decided to implement Cisco MPLS TE tunnels…

Converting the OSPFv2 domain to IS-IS would simplify the number of IGP types but would still result in multiple IGP domains, each with its own link-state database, and would not solve the problem of distributing this consolidated information to a centralized system.

RSVP-TE extensions are used by IGPs to flood TE attributes within a single IGP domain, and RSVP-TE itself is a signaling protocol for tunnel setup, not a mechanism to export a consolidated view of multiple domains' TE information to an external system.

BGP Link-State (BGP LS, defined in RFC 7752) is a specialized BGP address family designed to collect and advertise link-state and Traffic Engineering (TE) information from IGP domains (such as IS-IS and OSPFv2) to external controllers or centralized path computation systems. This allows the centralized offline path calculation system to receive a comprehensive and unified view of the entire multi-domain network topology, including TE attributes, which is crucial for computing optimal MPLS TE tunnels across domain boundaries.

Mutual redistribution between IGP domains would allow routes to be exchanged, but it primarily deals with reachability information and does not propagate the detailed link-state and traffic engineering attributes necessary for a centralized system to perform constrained path calculations for MPLS TE tunnels.