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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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Overview of VLL

Overview of VLL

Definition

Virtual leased line (VLL) technology, also called Virtual Private Wire Service (VPWS), emulates leased lines on an IP network to provide a low-cost asymmetrical digital data network (DDN) service. It is a point-to-point (P2P) Layer 2 tunneling technology based on Multiprotocol Label Switching (MPLS), which allows the exchange of data packets between networks using different media. Figure 4-1 shows an example of VLL networking.

Figure 4-1 VLL networking

Purpose

  • In network development, various Layer 2 networks have been deployed and are still in use, for example, Ethernet, Asynchronous Transfer Mode (ATM), Frame Relay (FR), and High-level Data Link Control (HDLC) networks. These Layer 2 networks are isolated from one another because they use different Layer 2 protocols. However, there is an increasing demand for direct communication between different Layer 2 networks.
  • As Ethernet develops rapidly, more Ethernet connections are required between large cities or remote areas. Traditionally, service providers deploy direct leased lines or set up Layer 2 tunnels between two areas. (The Layer 2 tunnels are set up between Layer 2 switching devices.) This solution has a high cost and is difficult to maintain and extend in some areas.

Service providers need a solution to these problems. VLL technology is introduced to establish a compatible Layer 2 switching network that is cost effective and easy to maintain and extend. Based on MPLS technology, VLL allows multiple customers to share one leased line and creates an exclusive virtual channel for each customer on the shared line. On an Ethernet network, sites in different cities can communicate over a P2P VLL connection on an MPLS network, just like communicating within a virtual local area network (VLAN).

Since Ethernet has replaced most types of Layer 2 networks, VLL is rarely used for communication between different networks, but is widely used for Layer 2 transparent transmission.

VLL is an MPLS-based Layer 2 virtual private network (L2VPN) technology to directly transmit Layer 2 data. VLL establishes P2P VPN tunnels for P2P communication. However, P2P service eventually became insufficient to meet user requirements, and in response a point-to-multipoint (P2MP) technology, called Virtual Private LAN Service (VPLS) was developed. For details about VPLS, see VPLS Configuration.

Benefits

VLL brings the following benefits:
  • Extended network functions and service capabilities for carriers

    Carriers can use VLL and enhanced MPLS technologies, such as traffic engineering (TE) and quality of service (QoS), to provide users with differentiated services, meeting diversified user requirements.

  • Interconnection between networks using different Layer 2 protocols

    VLL allows an Internet service provider (ISP) network to provide connections and switching services using multiple Layer 2 protocols.

  • Higher scalability

    VLL uses label stacks to identify multiple virtual circuits (VCs) in one label switched path (LSP). Therefore, the P device only needs to maintain information about one LSP, improving system scalability.

  • Smaller maintenance workload

    VLL provides a method to establish VPNs in large-scale enterprises with large sites and many routes. P devices on the ISP networks only need to forward packets over tunnels on the public network according to MPLS labels and do not need to maintain any Layer 2 information.

  • Smooth network upgrade

    VLL is transparent to users; therefore, carriers can smoothly upgrade their traditional L2VPN networks, such as ATM and FR networks, to MPLS L2VPN networks, without affecting configurations on customer networks. The network upgrade does not affect user services, except for a brief period of data loss during network migration.

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Updated: 2019-04-03

Document ID: EDOC1100075353

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