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NE20E-S V800R010C10SPC500 Feature Description - MPLS 01

This is NE20E-S V800R010C10SPC500 Feature Description - MPLS
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CR-LSP Backup

CR-LSP Backup

On one tunnel, a CR-LSP used to protect the primary CR-LSP is called a backup CR-LSP.

A backup CR-LSP protects traffic on important CR-LSPs. If a primary CR-LSP fails, traffic switches to a backup CR-LSP.

If the ingress detects that a primary CR-LSP is unavailable, the ingress switches traffic to a backup CR-LSP. After the primary CR-LSP recovers, traffic switches back. Traffic on the primary CR-LSP is protected.

CR-LSP backup is performed in either of the following modes:

  • Hot standby: A backup CR-LSP is set up immediately after a primary CR-LSP is set up. If the primary CR-LSP fails, traffic switches to the backup CR-LSP. If the primary CR-LSP recovers, traffic switches back to the primary CR-LSP. Hot-standby CR-LSPs support best-effort paths.

  • Ordinary backup: A backup CR-LSP is set up after a primary CR-LSP fails. If the primary CR-LSP fails, a backup CR-LSP is set up and takes over traffic from the primary CR-LSP. If the primary CR-LSP recovers, traffic switches back to the primary CR-LSP.

    Table 4-11 lists differences between hot-standby and ordinary CR-LSPs.
    Table 4-11 Differences between hot-standby and ordinary CR-LSPs

    Item

    Hot Standby

    Ordinary Backup

    When a backup CR-LSP is established

    Created immediately after the primary CR-LSP is established.

    Created only after the primary CR-LSP fails.

    Path overlapping

    Whether or not a primary CR-LSP overlaps a backup CR-LSP can be determined manually. If an explicit path is allowed for a backup CR-LSP, the backup CR-LSP can be set up over an explicit path.

    Allowed to use the path of the primary CR-LSP in any case.

    Whether or not a best-effort path is supported

    Supported

    Not supported

  • Best-effort path

    The hot standby function supports the establishment of best-effort paths. If both the primary and hot-standby CR-LSPs fail, a best-effort path is established and takes over traffic.

    As shown in Figure 4-26, the primary CR-LSP uses the path PE1 -> P1 -> PE2, and the backup CR-LSP uses the path PE1 -> P2 -> PE2. If both the primary and backup CR-LSPs fail, PE1 triggers the setup of a best-effort path PE1 -> P2 -> P1 -> PE2.

    Figure 4-26 Schematic diagram for a best-effort path

    NOTE:

    A best-effort path does not provide reserved bandwidth for traffic. The affinity attribute and hop limit are configured as needed.

Hot-standby CR-LSP Switchover and Revertive Switchover Policy

Traffic can switch to a hot-standby CR-LSP in automatic or manual mode:
  • Automatic switchover: Traffic switches to a hot-standby CR-LSP from a primary CR-LSP when the primary CR-LSP goes Down. If the primary CR-LSP goes Up again, traffic automatically switches back to the primary CR-LSP. This is the default setting. You can determine whether to switch traffic back to the primary CR-LSP and set a revertive switchover delay time.
  • Manual switchover: You can manually trigger a traffic switchover. Forcibly switch traffic from the primary CR-LSP to a hot-standby CR-LSP before some devices on a primary CR-LSP are upgraded or primary CR-LSP parameters are adjusted. After the required operations are complete, manually switch traffic back to the primary CR-LSP.

Path Overlapping

The path overlapping function can be configured for hot-standby CR-LSPs. This function allows a hot-standby CR-LSP to use links of a primary CR-LSP. The hot-standby CR-LSP protects traffic on the primary CR-LSP.

Comparison Between CR-LSP Backup and Other Features

  • The difference between CR-LSP backup and TE FRR is as follows:

    • CR-LSP backup is end-to-end path protection for an entire CR-LSP.

    • Fast reroute (FRR) is a partial protection mechanism used to protect a link or node on a CR-LSP. In addition, FRR rapidly responds to a fault and takes effect temporarily, which minimizes the switchover time.

  • CR-LSP hot standby and TE FRR are used together.

    If a protected link or node fails, a point of local repair (PLR) switches traffic to a bypass tunnel. If the PLR is the ingress of the primary CR-LSP, the PLR immediately switches traffic to a hot-standby CR-LSP. If the PLR is a transit node of the primary CR-LSP, it uses a signaling to advertise fault information to the ingress of the primary CR-LSP, and the ingress switches traffic to the hot-standby CR-LSP. If the hot-standby CR-LSP is Down, the ingress keeps attempting to reestablish a hot-standby CR-LSP.

  • CR-LSP ordinary backup and TE FRR are used together.

    • The association is disabled.

      If a protected link or node fails, a PLR switches traffic to a bypass tunnel. Only after both the primary and bypass CR-LSPs fail, the ingress of the primary CR-LSP attempts to establish an ordinary backup CR-LSP.

    • The association is enabled (FRR in Use).

      If a protected link or node fails, a PLR switches traffic to a bypass tunnel. If the PLR is the ingress of the primary CR-LSP, the PLR attempts to establish an ordinary backup CR-LSP. If the ordinary backup CR-LSP is successfully established, the PLR switches traffic to the new CR-LSP. If the PLR is a transit node on the primary CR-LSP, the PLR advertises the fault to the ingress of the primary CR-LSP, the ingress attempts to establish an ordinary backup CR-LSP. If the ordinary backup CR-LSP is successfully established, the ingress switches traffic to the new CR-LSP.

      If the ordinary backup CR-LSP fails to be established, traffic keeps traveling through the bypass CR-LSP.

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Updated: 2019-01-03

Document ID: EDOC1100055123

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