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Configuring Multicast-Only Fast Reroute

 

You can configure multicast-only fast reroute (MoFRR) to minimize packet loss in a network when there is a link failure.

When fast reroute is applied to unicast streams, an upstream router preestablishes MPLS label-switched paths (LSPs) or precomputes an IP loop-free alternate (LFA) fast reroute backup path to handle failure of a segment in the downstream path.

In multicast routing, the traffic distribution graphs are usually originated by the receiver. This is unlike unicast routing, which usually establishes the path from the source to the receiver. Protocols that are capable of establishing multicast distribution graphs are PIM (for IP), multipoint LDP (for MPLS) and RSVP-TE (for MPLS). Of these, PIM and multipoint LDP receivers initiate the distribution graph setup, and therefore:

  • On the QFX series, MoFRR is supported in PIM domains.

  • On the MX Series and SRX Series, MoFRR is supported in PIM and multipoint LDP domains.

The configuration steps are the same for enabling MoFRR for PIM on all devices that support this feature, unless otherwise indicated. Configuration steps that are not applicable to multipoint LDP MoFRR are also indicated.

(For MX Series routers only) MoFRR is supported on MX Series routers with MPC line cards. As a prerequisite,all the line cards in the router must be MPCs.

To configure MoFRR on routers or switches:

  1. (For MX Series and SRX Series routers only) Set the router to enhanced IP mode.
  2. Enable MoFRR.
  3. (Optional) Configure a routing policy that filters for a restricted set of multicast streams to be affected by your MoFRR configuration.

    You can apply filters that are based on source or group addresses.

    For example:

  4. (Optional) If you configured a routing policy to filter the set of multicast groups to be affected by your MoFRR configuration, apply the policy for MoFRR stream protection.

    For example:

  5. (Optional) In a PIM domain with MoFRR, allow MoFRR to be applied to any-source multicast (ASM) (*,G) joins.

    This is not supported for multipoint LDP MoFRR.

  6. (Optional) In a PIM domain with MoFRR, allow only a disjoint RPF (an RPF on a separate plane) to be selected as the backup RPF path.

    This is not supported for multipoint LDP MoFRR. In a multipoint LDP MoFRR domain, the same label is shared between parallel links to the same upstream neighbor. This is not the case in a PIM domain, where each link forms a neighbor. The mofrr-disjoint-upstream-only statement does not allow a backup RPF path to be selected if the path goes to the same upstream neighbor as that of the primary RPF path. This ensures that MoFRR is triggered only on a topology that has multiple RPF upstream neighbors.

  7. (Optional) In a PIM domain with MoFRR, prevent sending join messages on the backup path, but retain all other MoFRR functionality.

    This is not supported for multipoint LDP MoFRR.

  8. (Optional) In a PIM domain with MoFRR, allow new primary path selection to be based on the unicast gateway selection for the unicast route to the source and to change when there is a change in the unicast selection, rather than having the backup path be promoted as primary. This ensures that the primary RPF hop is always on the best path.

    When you include the mofrr-primary-selection-by-routing statement, the backup path is not guaranteed to get promoted to be the new primary path when the primary path goes down.

    This is not supported for multipoint LDP MoFRR.