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Configuration Guide - VPN

CloudEngine 12800 and 12800E V200R005C10

This document describes the configurations of VPN, including GRE, BGP/MPLS IP VPN, BGP/MPLS IPv6 VPN, VLL, PWE3, and VPLS.
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VPLS Fundamentals

VPLS Fundamentals

Basic VPLS Transport Structure

Figure 6-2 shows an example of a VPLS network. The entire VPLS network is similar to a switch. PWs are established over MPLS tunnels between VPN sites to transparently transmit Layer 2 packets between sites. When forwarding packets, Provider edges (PEs) learn the source MAC addresses of these packets and create MAC entries, mapping MAC addresses to attachment circuits (ACs) and pseudo wires (PWs).

The following table describes the various concepts related to VPLS networks.

Table 6-1 Description of VPLS concepts

Name

Description

AC

A link between a CE and a PE.

PW

A bidirectional virtual connection between two virtual switch instances (VSIs) residing on two PEs. A PW consists of a pair of unidirectional MPLS VCs transmitting in opposite directions.

VSI

A virtual switching unit on the switch for each VPLS. Each VSI has an independent MAC address table and a forwarder. A VSI is responsible for terminating PWs.

PW signaling

A type of signaling used to create and maintain PWs. PW signaling is the foundation for VPLS implementation. Currently, the PW signaling is Label Distribution Protocol (LDP).

Tunnel

A connection between a local PE and a remote PE used to transparently transmit data between PEs. A tunnel can carry multiple PWs and the tunnel type can be Label Switched Path (LSP).

Forwarder

Similar to a VPLS forwarding table. After a PE receives packets from an AC, the forwarder of the PE selects a PW to forward these packets.

Figure 6-2 Basic VPLS transmission process

The following uses the unicast packets sent from CE1 to CE3 in VPN1 as an example to describe how a data flow is transmitted on a VPLS network.

  1. PE1, PE2, and PE3 belong to the same VPLS domain. AC links connected to the VPLS domain are mapped to PWs through a VSI to generate the forwarder of the VSI.
  2. When CE1 receives a Layer 2 packet from a user at Site1, it forwards the Layer 2 packet to PE1 through the AC link.
  3. After receiving the packet, PE1 finds that the packet needs to be forwarded in VPLS mode. PE1 then selects a PW from the forwarder to forward the packet based on the destination MAC address of the packet.
  4. PE1 generates double labels according to the forwarding entry of the PW. The inner private network label identifies the PW, and the outer public network label enables the packet to reach PE2 through the tunnel on the public network. Meanwhile, PE1 searches for the destination MAC address based on the MAC address table index and encapsulates the packet.
  5. After the Layer 2 packet arrives at PE2 through the tunnel on the public network, the private network label becomes the outer label (the public network label has been popped out at the penultimate hop).
  6. Upon receiving the packet, PE2 selects a VSI for forwarding the packet according to the private network label, removes the private network label, and selects the forwarder of the VSI. The forwarder forwards the Layer 2 packet to CE3 according to the destination MAC address.

VPLS Implementation Process

Transmission of packets between Customer Edges (CEs) relies on VSIs configured on PEs, and PWs established between the VSIs. Figure 6-3 shows transmission of Ethernet frames over full-mesh PWs between PEs.

Figure 6-3 VPLS forwarding model

A VPLS network consists of a control plane and a forwarding plane.

  • The control plane of a VPLS PE provides the PW establishment function, including:

    • Member discovery: a process in which a PE in a VSI discovers the other PEs in the same VSI. This process can be implemented manually.
    • Signaling mechanism: PWs between PEs in the same VSI are established, maintained, or torn down using signaling protocols.
  • The forwarding plane of a VPLS PE provides the data forwarding function, including:

    • Encapsulation: After receiving Ethernet frames from a CE, a PE encapsulates the frames into packets and sends the packets to VPLS network.
    • Forwarding: A PE determines how to forward a packet based on the inbound interface and destination MAC address of the packet.
    • Decapsulation: After receiving packets from VPLS network, a PE decapsulates these packets into Ethernet frames and sends the frames to a CE.
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Updated: 2019-04-03

Document ID: EDOC1100075353

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