Which transport-layer protocol carries LDP sessions?
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Correct answer: TCP.
Why this is the answer
LDP (Label Distribution Protocol) uses TCP port 646 for establishing and maintaining sessions between LDP peers. TCP provides reliable, ordered, and error-checked delivery of LDP messages, which is crucial for the consistent exchange of label mappings necessary for MPLS forwarding. UDP is connectionless and unreliable, making it unsuitable for the session-oriented nature of LDP. SCTP (Stream Control Transmission Protocol) is a newer transport protocol offering features like multi-homing and multi-streaming, but it is not the standard transport for LDP. RDP (Remote Desktop Protocol) is an application-layer protocol for remote access, unrelated to LDP.
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