LDP-Signaled Layer 2 Circuits

BC

LDP (Label Distribution Protocol) is a signaling protocol used for distributing labels between routers to establish LSPs (Label Switched Paths) for MPLS (Multiprotocol Label Switching) networks. LDP can also be used to signal Layer 2 circuits, such as Ethernet or ATM virtual circuits, between PE (Provider Edge) routers in a Layer 2 VPN (Virtual Private Network).

Regarding LDP-signaled Layer 2 circuits, the following statements are correct:

A. You must enable the Layer 2 VPN signaling NLRI: The NLRI (Network Layer Reachability Information) is a type of BGP (Border Gateway Protocol) message used to advertise VPN routes. To enable LDP-signaled Layer 2 circuits, the Layer 2 VPN signaling NLRI must be enabled on the PE routers so that they can exchange BGP messages containing the Layer 2 circuit information.

B. You must configure the virtual circuit identifier: The virtual circuit identifier (VC ID) is a value used to identify the specific Layer 2 circuit being signaled by LDP. The VC ID is unique within a given PE router, and it must be configured manually on each PE router for each Layer 2 circuit.

C. You must specify the neighbor using the tunnel end-point IP address: To establish an LDP-signaled Layer 2 circuit, the PE routers must exchange LDP messages containing information about the circuit. To do this, the PE routers must know each other's IP addresses. Typically, the PE routers are connected by a Layer 3 network, and they use the tunnel end-point IP addresses to specify each other as LDP neighbors.

D. You must define a unique site-identifier value: The site identifier (Site-ID) is a value used to distinguish between Layer 2 circuits that have the same VC ID on different PE routers. The Site-ID is unique within a given VPN, and it must be configured manually on each PE router for each Layer 2 circuit. The Site-ID is used in combination with the VC ID to form a globally unique identifier for the Layer 2 circuit.

In summary, to establish an LDP-signaled Layer 2 circuit, you must enable the Layer 2 VPN signaling NLRI, configure the VC ID and Site-ID values, and specify the LDP neighbor using the tunnel end-point IP address.