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CLI-based Configuration Guide - VPN

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document describes VPN features on the device and provides configuration procedures and configuration examples.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
VLL FRR

VLL FRR

Widespread adoption of MPLS L2VPN technologies has raised high reliability requirements for L2VPNs, especially for L2VPNs that carry real-time services such as VoIP and IPTV.

Virtual Lease Line Fast Reroute (VLL FRR) uses redundant networking to improve MPLS L2VPN reliability. When a PW or PE device fails, VLL FRR fast switches traffic to a backup link. This mechanism implements end-to-end fault detection on PWs and provides PW protection, greatly improving link-layer reliability for MPLS L2VPNs.

Figure 10-11 shows the application of VLL FRR in asymmetrical CE deployment: the CE device is connected to one PE device at one end while the CE device is dual-homed to two PE devices at the other end.

Figure 10-11  Asymmetrical CE deployment

In asymmetrical networking, PE1 or CE2 is the failover point and the last step in the fault notification process. When the primary link fails, PE1 in the single-homed site detects the fault, triggers traffic switching, and does not send fault notification to CE1. When the primary link in the dual-homed site fails, CE2 receives the fault notification from the PE device on the primary link and switches traffic to the backup link.

VLL FRR Implementation

  • Fault Detection

    When a fault occurs on the VLL network, devices can detect link failures through route convergence. However, the detection speed is slow and cannot meet the requirements of delay-sensitive services, such as VoIP services. To improve the fault detection speed, you can deploy Bidirectional Forwarding Detection (BFD) on the PE device to rapidly detect PW failures. BFD has a low cost and can implement millisecond-level fault detection.

  • Switching Between Primary and Backup PWs

    You can set up a backup PW on the VLL network. When the primary PW is working properly, the backup PW does not transmit data. When the primary PW is faulty, data is switched to the backup PW. The backup PW remains in Up state to ensure fast traffic switching when the primary PW fails, preventing traffic loss.

    As shown in Figure 10-12, PE1-P1-PE2 is the primary link and PE1-P2-PE3 is the backup link. When the system detects that the primary PW or PE2 is faulty, PE1 performs switching between primary and backup PWs to import traffic to the backup PW, ensuring traffic transmission from CE1 to CE2.

    Figure 10-12  Switching between primary and backup PWs

  • Fast Fault Notification

    As shown in Figure 10-12, switching between primary and backup PWs ensures normal traffic transmission from CE1 to CE2, while switching of traffic from CE2 to CE1 is ensured by fast fault notification.

    The OAM mapping between a PW and an AC interface can be created. In this manner, when a PW or a PE is faulty, a CE can take measures in time to fast switch traffic to a secondary path. The OAM messages are transparently transmitted on a PW. This enables the PW with the end-to-end fault detection function.
    • AC Fault Detection and Notification Mechanism

      As shown in Figure 10-13, in the scenario where a fault occurs on an AC between CE1 and PE1, the fault detection and notification mechanism works as follows:

      1. AC OAM on PE1 detects an AC fault.

      2. According to the OAM mapping on the PE1, the PW status corresponding to the AC is updated.

      3. BFD transparently sends an OAM fault message to PE2.

      4. When PE2 receives the BFD fault message, if a secondary PW is set up on the remote PE, the traffic switchover is performed. Otherwise, OAM mapping is performed and then the faulty AC is notified to CE2.

      Figure 10-13  AC fault detection and notification mechanism

    • PSN Fault Detection and Notification Mechanism

      As shown in Figure 10-14, when a fault occurs in a packet switched network (PSN), the fault detection and notification mechanism works as follows:

      1. The BFD session on the PE detects a fault in the PSN.

      2. The PE obtains the local AC according to the OAM mapping.

      3. If a secondary PW is set up, the traffic switchover is performed; otherwise, the OAM mapping is performed and the corresponding AC is mapped and the fault is notified to the local CE.

      Figure 10-14  PSN fault detection and notification mechanism

  • PW Switchback Policy

    In the networking of CEs asymmetrically accessing PEs, when PE1 is notified of fault removal on the primary PW, PE1 works based on the PW switchback policy.

    The PW switchback policies are as follows:

    • No switchback: Traffic is not switched back to the primary PW.

    • Immediate switchback: Traffic is immediately switched back to the primary PW.

    • Delayed switchback: Traffic is switched back to the primary PW after a delay period.

    After the switchback, the PE immediately notifies the peer PE on the secondary PW of the fault. In addition, after a delay period or immediately the PE notifies the peer PE on the secondary PW of fault removal, which prevents packet loss due to transmission delay between PEs.

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Updated: 2019-08-07

Document ID: EDOC1100033725

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