Which of the following statements regarding LSPs are true? (Choose two)

Statement A is correct because LDP, a common protocol for establishing LSPs, determines the path for a Forwarding Equivalence Class (FEC) by following the best path determined by the Interior Gateway Protocol (IGP), which is stored in the routing table.
Statement B is correct as it accurately describes a constraint-based routed LSP, typically signaled using RSVP-TE. The ingress Label Edge Router (LER) calculates the entire path using the Constrained Shortest Path First (CSPF) algorithm. This calculation relies on a traffic engineering database (TED), which is more detailed than a standard routing table, and considers user-defined constraints like bandwidth and administrative groups.

C. The path for a constraint-based routed LSP is calculated once at the ingress node, not re-calculated at each hop. Each-hop calculation is characteristic of standard IP forwarding.
D. IGP-based LSPs, most commonly established by LDP, follow the IGP path. However, it is not a requirement that they must use LDP signaling.

1. Nokia 7750 SR OS MPLS Guide, Release 21.10.R1, Section: LDP. "LDP associates a set of destinations (FECs) with an LSP. The path of an LDP LSP is determined by the routing table."

2. Nokia 7750 SR OS MPLS Guide, Release 21.10.R1, Section: RSVP-TE. "For a constraint-based LSP, the path is computed by the ingress LER based on a number of constraints. The ingress LER uses a traffic engineering database (TED) to perform the path computation."