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Feature Description - VPN 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - VPN
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PW Redundancy

PW Redundancy

PW Redundancy Signaling

In conventional pseudo wire emulation edge-to-edge (PWE3), one-to-one mapping is implemented between ACs and PWs. To ensure the same forwarding capability, the PW protection mechanism to be used must allow the configuration of a single PW in a PW group as an active PW and the remaining as inactive PWs.

Relevant standards, Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP), specifies the PW Status type-length-value (TLV) to transmit the PW forwarding status. The PW Status TLV is transported to the remote PW peer using a Label Mapping or LDP Notification message. The PW Status TLV is a 32-bit status code field. Each bit in the status code field can be set individually to indicate more than a single failure at once. PW redundancy introduces a new PW status code, 0x00000020. When the code is set, it indicates "PW forwarding standby".


Only PWE3 VPWS supports PW redundancy.

Primary/Secondary and Active/Inactive PWs

PW redundancy involves the following terms:

  • Primary/secondary

    Primary and secondary are terms used to describe PW forwarding priorities and can be configured. A PE selects the primary PW in preference to a secondary PW when both PWs are in the Active state. Currently, only one secondary PW can be configured for a primary PW. Note that a bypass PW can also be regarded as a secondary PW.

  • Active/standby

    Active and standby are terms used to describe PW forwarding and operating status and cannot be configured. Only active PWs are used to forward traffic. The signaling status and configured forwarding priority determine PW forwarding status. A PW with the highest priority will be selected as an active PW to forward traffic. All the other PWs will be in the standby state and must not be used to forward traffic. Standby PWs used in VPWS can be configured to receive traffic though.

PW Redundancy Modes

PW redundancy modes are specified on PEs where primary and secondary PWs have been configured. If the PW redundancy mode is not specified, PWE3 fast reroute (FRR) will be used.


In PWE3 FRR, a PE locally determines the primary and secondary status of PWs without informing the remote PE of the status. PWE3 FRR is implemented on Huawei devices only and is not recommended.

PW redundancy operates in either of the following modes:


A PE locally determines the primary and secondary status of the PWs, and uses signaling to inform a remote PE of the status. The PW status is independent of the AC status, and therefore PW and AC failures are isolated.


On a PE, its PW status is determined by the remote AC status after negotiation procedures. The remote PE then informs the PE of the PW status. If an AC fails and protection switching is triggered, protection switching will also be implemented on the PWs. This mode cannot isolate PW and AC failures.


The independent PW redundancy mode is recommended in PWE3 networking to ensure protection switching.

PW Redundancy Usage Scenarios

3PE PW redundancy

Figure 6-24 3PE PW redundancy

  • E-Trunk 1:1 protection.

  • Supported Master/Slave Mode,Bypass PWs can be configured.

  • Supported Independent Mode.Bypass PWs can be configured.

4PE PW redundancy

Figure 6-25 4PE PW redundancy

  • VRRP or E-Trunk 1:1 protection.

  • Not supported Master/Slave Mode.

  • Supported Independent Mode.

  • Dual bypass PWs can be configured, but only Ethernet services are allowed.
    • Dual bypass PWs do not support heterogeneous interworking.

    • Dual bypass PWs do not support VPN QoS.

    • Dual bypass PWs do not support link fault detection.

Updated: 2019-01-14

Document ID: EDOC1100058940

Views: 16816

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