Vpls For An Mpls-Based Provider Core; Hierarchical Vpls - Cisco CRS Configuration Manual
Ios xr virtual private network
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Multipoint Layer 2 Services Overview
Multipoint Layer 2 services are also called as Virtual Private LAN Services.
Note
Multipoint Layer 2 Services transports Ethernet 802.3, VLAN 802.1q, and VLAN-in-VLAN (Q-in-Q) traffic
across multiple sites that belong to the same Layer 2 broadcast domain. It offers simple Virtual LAN services
that include flooding broadcast, multicast, and unknown unicast frames that are received on a bridge. The
Multipoint Layer 2 Services solution requires a full mesh of pseudowires that are established among provider
edge (PE) routers. The Multipoint Layer 2 Services implementation is based on Label Distribution Protocol
(LDP)-based pseudowire signaling.
A VFI is a virtual bridge port that is capable of performing native bridging functions, such as forwarding,
based on the destination MAC address, source MAC address learning and aging.
After provisioning attachment circuits, neighbor relationships across the MPLS network for this specific
instance are established through a set of manual commands identifying the end PEs. When the neighbor
association is complete, a full mesh of pseudowires is established among the network-facing provider edge
devices, which is a gateway between the MPLS core and the customer domain.
The service provider network starts switching the packets within the bridged domain specific to the customer
by looking at destination MAC addresses. All traffic with unknown, broadcast, and multicast destination MAC
addresses is flooded to all the connected customer edge devices, which connect to the service provider network.
The network-facing provider edge devices learn the source MAC addresses as the packets are flooded. The
traffic is unicasted to the customer edge device for all the learned MAC addresses.
Multipoint Layer 2 Services require the provider edge device to be MPLS-capable. The Multipoint Layer 2
Services provides edge device holds all the VPLS forwarding MAC tables and Bridge Domain information.
In addition, it is responsible for all flooding broadcast frames and multicast replications.
VPLS for an MPLS-based Provider Core
VPLS is a multipoint Layer 2 VPN technology that connects two or more customer devices using bridging
techniques. The VPLS architecture allows for the end-to-end connection between the Provider Edge (PE)
routers to provide Multipoint Ethernet Services.
VPLS requires the creation of a bridge domain (Layer 2 broadcast domain) on each of the PE routers. The
access connections to the bridge domain on a PE router are called attachment circuits (AC).
The attachment circuits can be a set of physical ports, virtual ports, or both that are connected to the bridge
at each PE device in the network.
The MPLS/IP provider core simulates a virtual bridge that connects the multiple attachment circuits on each
of the PE devices together to form a single broadcast domain. A VFI is created on the PE router for each
VPLS instance. The PE routers make packet-forwarding decisions by looking up the VFI of a particular VPLS
instance. The VFI acts like a virtual bridge for a given VPLS instance. More than one attachment circuit
belonging to a given VPLS are connected to the VFI. The PE router establishes emulated VCs to all the other
PE routers in that VPLS instance and attaches these emulated VCs to the VFI. Packet forwarding decisions
are based on the data structures maintained in the VFI.
Hierarchical VPLS
Hierarchical VPLS (H-VPLS) is an extension of basic VPLS that provides scaling and operational benefits.
H-VPLS provides a solution to deliver Ethernet multipoint services over MPLS. H-VPLS partitions a network
into several edge domains that are interconnected using an MPLS core. The use of Ethernet switches at the
Cisco IOS XR Virtual Private Network Configuration Guide for the Cisco CRS Router, Release 6.1.x
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Implementing Multipoint Layer 2 Services
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