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Configuring VPLS
Overview
Virtual Private LAN Service (VPLS), also called "Transparent LAN Service" or "virtual private
switched network service," can deliver a point-to-multipoint L2VPN service over public networks.
With VPLS, geographically-dispersed sites can interconnect and communicate over MAN or WAN as
if they were on the same LAN.
VPLS provides Layer 2 VPN services. However, it supports multipoint services rather than the
point-to-point services the traditional VPN supports. With VPLS, service providers can create a
series of virtual switches for customers on the PEs, allowing customers to build their LANs across
the MAN or WAN.
Operation of VPLS
The following are some basic concepts of VPLS:
•
CE
—Customer edge device directly connected to the service provider network.
•
PE
—Provider edge device connecting one or more CEs to the service provider network. A PE
maps and forwards packets between private networks and public network tunnels. A PE can be
a UPE or NPE.
•
UPE
—User facing provider edge device that functions as the user access convergence device.
•
NPE
—Network provider edge device that functions as the network core PE. An NPE resides at
the edge of a VPLS network core domain and provides transparent VPLS transport services
between core networks.
•
VSI
—Virtual switch instance that maps actual access links to virtual links.
•
PW
—Pseudo wire, a bidirectional virtual connection between VSIs. A PW consists of two
unidirectional MPLS VCs.
•
AC
—Attachment circuit connecting the CE to the PE. It can use physical interfaces or virtual
interfaces. Usually, all user packets on an AC, including Layer 2 and Layer 3 protocol messages,
must be forwarded to the peer site without being changed.
•
QinQ
—802.1Q in 802.1Q, a tunneling protocol based on 802.1Q. It offers a point-to-multipoint
L2VPN service mechanism. With QinQ, the private network VLAN tags of packets are
encapsulated into the public network VLAN tags, allowing packets to be transmitted with two
layers of tags across the service provider network. This provides a simpler Layer 2 VPN
tunneling service.
•
Forwarders
—A forwarder functions as the VPLS forwarding table. Once a PE receives a
packet from an AC, the forwarder selects a PW for forwarding the packet.
•
Tunnel
—A tunnel, usually an MPLS tunnel, is a direct channel between a local PE and the peer
PE for transparent data transmission in-between. It is used to carry PWs. A tunnel can carry
multiple PWs.
•
Encapsulation
—Packets transmitted over a PW use the standard PW encapsulation formats
and technologies: Ethernet and VLAN.
•
PW
signaling
—The PW signaling protocol is the fundament of VPLS. It is used for creating and
maintaining PWs and automatically discovering VSI peer PEs. Two PW signaling protocols are
available: LDP and BGP.