Which protocol is used to signal the service label for a Layer 3 VPRN service?

In a Layer 3 VPRN service based on RFC 4364, Multi-Protocol BGP (MP-BGP) is the control plane protocol responsible for distributing VPN routing information between Provider Edge (PE) routers. When a PE router advertises a VPN-IPv4 prefix to its MP-BGP peers, it includes a unique MPLS label. This label, known as the service label or VPN label, is used by the receiving PE router to identify the correct VPN Routing and Forwarding (VRF) instance to which the incoming packet belongs. This mechanism allows for the segregation and proper forwarding of traffic from different VPRNs.

A. L-LDP is not a standard protocol for signaling service labels. LDP (Label Distribution Protocol) is used for transport labels, not VPRN service labels.
B. T-LDP (Targeted LDP) is the signaling protocol used to exchange service (VC) labels for Layer 2 VPN services like VPLS and Epipe, not for Layer 3 VPRN services.
C. RSVP-TE is a protocol used to establish traffic-engineered Label Switched Paths (LSPs). It signals the transport label for the tunnel, not the VPRN service label.

Nokia 7750 SR OS MPLS Guide, Release 21.10.R1, "Layer 3 VPN (VPRN)" chapter, Section: "VPRN Service Overview". The guide states, "When MP-BGP distributes a VPN-IPv4 route, it also distributes an MPLS label for that route. This label is used by the far-end PE to direct traffic to the correct VPRN service."

IETF RFC 4364, "BGP/MPLS IP Virtual Private Networks (VPNs)", Section 4. This RFC is the foundational standard for VPRNs and specifies the use of MP-BGP to distribute VPN-IPv4 routes along with an MPLS label.

Nokia SRC-PE Self-Study Guide, Volume 1, Module 3: Virtual Private Routed Networks. This courseware explains that MP-BGP is used to advertise VPN-IPv4 prefixes and their associated VPN labels between PE routers.