For the data packets in a VPRN, how is the inner label in an MPLS packet signaled?

In a Virtual Private Routed Network (VPRN), a two-label stack is used to forward customer traffic across the provider's MPLS core. The inner label, often called the VPN or service label, is crucial for the egress PE router to identify which specific VPRN instance (and its corresponding Virtual Routing and Forwarding table, or VRF) the incoming packet belongs to. This inner label is allocated by the egress PE and advertised to other PE routers along with the customer's VPN-IPv4 prefixes. The signaling protocol used for this exchange of routing information and labels between PE routers is Multi-Protocol BGP (MP-BGP).

A: The inner label identifies the customer VPRN on the egress PE, not the egress PE itself. The outer (transport) label identifies the egress PE.

B: Targeted LDP (T-LDP) is a signaling protocol primarily used for Layer 2 VPN services like VPLS, not for distributing VPRN service labels.

D: RSVP and LDP are used to signal the outer (transport) label for the Label Switched Path (LSP) that directs traffic to the egress PE.

E: While the purpose is correct (identifying the customer VPRN), the signaling protocols listed (RSVP and LDP) are used for the outer transport label.

1. Nokia 7750 SR OS Services Architecture Guide, Release 21.10.R1, "VPRN Services" chapter, Section: "VPRN Control and Data Planes": This section details the VPRN architecture. It states, "MP-BGP is the routing protocol used to distribute customer routes and exchange information between the PE routers... When the egress PE receives the customer routes from a CE, it adds the route distinguisher to make the route unique and advertises it to other PE routers using MP-BGP. The egress PE also allocates a unique VPN label for the route and includes it in the MP-BGP update." This confirms MP-BGP signals the VPN (inner) label.

2. Nokia 7750 SR OS Services Architecture Guide, Release 21.10.R1, "VPRN Services" chapter, Section: "Packet Walk-through": This section illustrates the forwarding process. It describes how the egress PE, upon receiving a packet, pops the outer (transport) label and uses the inner (VPN) label to "determine which VPRN instance the packet belongs to" and performs a lookup in the corresponding VRF. This confirms the function of the inner label is to identify the customer VPRN.