Which statement about RSVP-signaled LSPs is correct?

In a Juniper Networks environment,Resource Reservation Protocol (RSVP)is a signaling protocol used to establish Label-Switched Paths (LSPs). While RSVP handles the actual signaling (requesting labels and reserving bandwidth along a path), it does not inherently know which path to take. This is whereConstrained Shortest Path First (CSPF)comes into play.

CSPFis an advanced version of the Dijkstra algorithm used specifically for traffic engineering. Unlike the standard SPF used by IGPs, which only considers the shortest metric, CSPF takes into account multiple constraints such as available bandwidth, link coloring (administrative groups), and explicit hop requirements. According to Juniper technical documentation, when an LSP is configured, the Ingress router uses CSPF to calculate a loop-free path that satisfies all these constraints before RSVP begins signaling. This is why statementBis the correct description of the operational flow.

StatementDis a common distractor. While CSPF uses theTraffic Engineering Database (TED)to perform its calculations, the path is not "calculated by the TED" itself; the TED is merely the repository of link-state information (provided by OSPF or IS-IS extensions). StatementCrefers to Segment Routing Global Block (SRGB), which is relevant to Segment Routing (SR-TE), not standard RSVP-signaled LSPs. Finally, statementAis incorrect because admin-groups (link coloring) are actually one of the primary constraints thatrequireCSPF to determine a valid path.