This article explains the scenario where an FPC on a MX router goes offline due to reduced switch fabric bandwidth. It covers the underlying cause, symptom, and recommended corrective actions.

On MX platforms, each FPC relies on full participation from all CBs in the chassis to access the required switch fabric bandwidth. If one of the CBs fails or becomes partially unavailable, the system may reduce the effective fabric bandwidth. High-capacity FPCs (such as MPC10E) can be configured with the setting:

  fpc 10 {

    offline-on-fabric-bandwidth-reduction;

    }

This configuration causes the FPC to automatically go offline and generate an alarm if the available fabric bandwidth drops below the threshold required for reliable forwarding.

2026-02-05 23:48:09 UTC Minor CB 2 LTC Device Fail

2026-02-05 23:48:09 UTC Minor CB 2 PMBus Device Fail

2026-02-05 23:47:47 UTC Major FPC 10 offlined due to reduced fabric BW

2026-02-05 23:47:42 UTC Minor CB 2 Retimer Sensor Fail

Check for any fabric issues or Control Board (CB) failures. If the effective fabric bandwidth is reduced due to a CB issue, the system will report an FPC alarm.

Once the CB issue is resolved, the FPC is excepted to recover.

2026-02-09 : Article Created

2026-06-15 : Mark to be external