Which of the following about an established LDP session is TRUE?

The Label Distribution Protocol (LDP) uses two transport mechanisms. For neighbor discovery, it sends UDP-based Hello messages to the "all routers on this subnet" multicast address (224.0.0.2) using the well-known port 646. However, for the actual LDP session, where label mappings and other notifications are exchanged, LDP establishes a reliable TCP connection. This TCP connection is established to the well-known LDP port, which is 646. The use of TCP ensures the reliable, in-order delivery of critical label information between LDP peers.

A. The LDP session uses TCP for reliability, not UDP, and the destination port is well-known, not arbitrary.
B. UDP is used for LDP discovery (Hellos), not for the established session that exchanges label mappings.
C. The destination port for the LDP TCP connection is the well-known port 646, not an arbitrary port.

RFC 5036, "LDP Specification", Section 2.5.2, "Transport Connection". It explicitly states, "LDP uses TCP for session communication. The well-known TCP port 646 has been assigned by IANA for LDP."

Nokia 7750 SR OS MPLS Guide, Release 21.10.R1, "LDP Overview". The guide describes the LDP session establishment process, noting the use of TCP on port 646 for the session itself.