H3C Technologies H3C SR8800 - Manual (Page 164)

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Configuring VPLS
VPLS overview
Virtual Private LAN Service (VPLS), also called Transparent LAN Service (TLS) 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 that traditional VPN supports. With VPLS, service providers can create on the PEs
a series of virtual switches for customers, allowing customers to build their LANs across the Metropolitan
Area Network (MAN) or Wide Area Network (WAN).
Operation of VPLS
Basic VPLS concepts
• CE—Customer edge device that is directly connected to the service provider network.
• PE—Provider edge device that connects 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 that is the bidirectional virtual connection between VSIs. A PW consists of two
unidirectional MPLS virtual circuits (VCs).
• AC—Attachment circuit that connects 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.
• Forwarder—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.