This article explains the SIB fault due to PIO errors causing the device hung.

The device will show below;

Mar 19 08:26:53 SIB0_PF_0 pfchip_outqd_scan_error_reg: Detected outq Dat LLM SRAM corrected llm err.

Mar 19 08:26:53 pfchip_ccl_poll_error_registers: int_status reg read failed 0

Mar 19 08:26:53 pfchip_scan failed due to PIO errors

Mar 19 08:26:57 2026 QFX10002-60c chassisd[31286]: CHASSISD_FM_SIB_ERROR: Fabric management error for SIB 0: Set SIB to FAULT (Fault due to PIO errors)

Mar 19 08:26:57 2026 QFX10002-60c alarmd[31289]: Alarm set: SIB id=16777332, color=RED, class=CHASSIS, reason=SIB 0 Fault

Mar 19 08:26:57 2026 QFX10002-60c craftd[31333]: Receive FX craftd set alarm message: color: 1 class: 100 object: 116 slot: 0 silent: 0 short_reason=SIB 0 Fault long_reason=SIB 0 Fault id=16777332 reason=16777216

Mar 19 08:26:57 2026 QFX10002-60c craftd[31333]: Major alarm set, SIB 0 Fault

Mar 19 08:26:57 2026 QFX10002-60c chassisd[31286]: CHASSISD_FRU_TO_SNMP_INDEX_ERROR: snmp_fru_to_bidx: fru_name:SIB: fru_type:8

user@QFX10002-60c> show chassis alarms no-forwarding

2 alarms currently active

Alarm time    Class Description

2026-02-26 19:39:27 UTC Minor SIB 0 Not Online

2026-02-26 19:27:35 UTC Major FPC 0 offlined due to unreachable destinations

user@QFX10002-60c> show chassis fpc detail

Slot 0 information:

 State        Offline

 Reason        FPC offlined due to unreachable destinations

 Error code      2164244

 Temperature      38 degrees C / 100 degrees F

 Total CPU DRAM     32768 MB

 Total SRAM      0 MB

 Total SDRAM      0 MB

Fabric reachability status: Unreachable destinations removed

Fabric reachability detection:

 Unreachable destinations    : Present on 1 FPCs

  Detected on       : 2026-02-26 19:27:25 UTC

  Reason        : Fabric plane error

Fabric reachability action:

 Fabric reachability action    : FPC action

 Acting on        : Fabric plane error

 Initial phase       : SIB restart

 Current phase       : FPC offline is completed

 Action started       : 2026-02-26 19:27:10 UTC

 Action completed      : 2026-02-26 19:27:34 UTC

Fabric reachability resolution: Unreachable destinations removed after phase FPC offline

user@QFX10002-60c>

On certain PF chip correctable errors, sib is going to fault and resulting FPC/interfaces to go down.
This error detection was enabled in 22.4 release. These errors are rare and can occur without any external trigger.
This behaviour has been rectified in 24.4 release. With this rectification, these PF chip correctable errors no longer result in SIB faults.

Please see below PR for more details:

https://prsearch.juniper.net/problemreport/PR1945957