Which protocol should be secured with MD5 authentication across the MPLS cloud to prevent insertion of bogus routers?

LDP (Label Distribution Protocol) is used to distribute labels in an MPLS network. Securing LDP with MD5 authentication prevents unauthorized routers from forming LDP adjacencies and injecting bogus label mappings, which could lead to traffic misdirection or denial-of-service attacks within the MPLS cloud. RSVP (Resource Reservation Protocol) is used for traffic engineering and can also be secured, but its primary role isn't label distribution for basic forwarding. LSP (Label Switched Path) is a path, not a protocol, so it cannot be secured directly. MP-BGP (Multiprotocol BGP) is used for VPNv4/VPNv6 label distribution in MPLS VPNs, but LDP is fundamental for the underlying MPLS label distribution between routers.