4.1.h Describe basic L2VPN — LAN services

  • 4.1.h [i] MPLS-VPLS general principals

VPLS is a technology that allows Multiprotocol Label Switching (MPLS) networks to offer Layer 2 Ethernet services. It provides multipoint Ethernet service as compared to Ethernet over MPLS (EoMPLS) that is point to point. VPLS emulates a virtual IEEE Ethernet bridge network . It uses flooding to communicate MAC address reachability information. VPLS can carry single VLAN within each instance. It supports MAC address aging and replicates broadcast and multicast traffic. A point to point Ethernet Virtual Circuit (EVC) connecting a pair of physical UNIs is also known as Ethernet Wire Service (EWS) or Ethernet Private Line (EPL). EPL provides VLAN transparency and control protocol tunneling are supplied by the implementation of 802.1Q-in-Q tag-stacking technology. Ethernet Virtual Private Line (EVPL) and EPL are also considered E-Line services.

Unlike Layer 3 VPN, there is no routing interaction between customer and service provider networks. ● Multipoint-to-multipoint configuration

● Forwarding of frames based on learned MAC addresses

● Uses virtual forwarding instance (VFI, like VLAN) for customer separation

VPLS Components:

● User-facing PE (U-PE): The U-PE is the device to which the functions needed to take forwarding or switching decisions at the ingress of the provider network.

● Network PE (N-PE): The N-PE is the device to which the signaling and control functions are allocated when a VPLS-PE is distributed across more than one box.

● Virtual switching instance (VSI): Virtual switching instance that serves one single VPLS A VSI performs standard LAN (that is, Ethernet) bridging functions, including forwarding done by a VSI based on MAC addresses and VLAN tags.

● Pseudowire (PW): PWE3 is a mechanism that emulates the essential attributes of a telecommunications service (such as a T1 leased line or Frame Relay) over a PSN.

● Attachment circuit (AC): The physical or virtual circuit attaching (AC) a CE to a PE. An attachment circuit may be, for example, a Frame Relay DLCI, an ATM VPI/ VCI, an Ethernet port, a VLAN, or an MPLS LSP. One or multiple ACs can belong to same VFI.

● VC (virtual circuit): Martini-based data encapsulation, tunnel label is used to reach remote PE, VC label is used to identify VFI. One or multiple VCs can belong to same VFI

Virtual Forwarding Instance (VFI):

● VFI creates L2 multipoint bridging among all ACs and VCs. It’s an L2 broadcast domain such as VLAN.

● Multiple VFIs can exist on the same PE box to separate user traffic such as VLANs.


Signaling uses LDP to establish and tear down PWs. Using LDP as the signaling VPLS control plane does not have inherent support of auto-discovery. Therefore , LDP -VPLS relies on manual configuration to identify all PE routers. MPLS in the core, normal LDP sessions per hop to exchange tunnel label or IGP label. Targeted or directed LDP session between PEs to exchange VC label. Tunnel label is used to forward packet from PE to PE VC label and is used to identify L2VPN circuit.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 4775-4779).  . Kindle Edition.