This article helps to resolve a Chassis Cluster 'down' issue, due to the Fabric Link failing to come up.

Check the output of the command 'show chassis cluster interfaces', and verify the 'Fabric link status'.

{primary:node0}
root@SRX_Branch> show chassis cluster interfaces
Control link 0 name: fxp1
Control link status: Up

Fabric interfaces:
Name Child-interface Status
fab0 ge-0/0/2 down
fab0
fab1 ge-9/0/2 down
fab1
Fabric link status: down

For a High End series SRX services gateway device:

{primary:node0}
root@SRX_HighEnd> show chassis cluster interfaces
Control link 0 name: em0
Control link 1 name: em1
Control link status: up

Fabric interfaces:
Name Child-interface Status
fab0 ge-0/0/5 down
fab0
Fabric link status: down


Follow the steps as given below to troubleshoot and fix the Fabric Link Status is showing down.

  Do you have a switch in between the two Chassis Cluster nodes for the Fabric Link?

• Yes - Continue to Step 2
• No   - Go to Step 3

  Remove the switch and try a direct connection between the Fabric Link ports. Now reboot the secondary node.

Are the Fabric Links still down?

• Yes  - Continue with Step 3.
• No  - This would mostly likely mean that there is an issue in the way the cluster was setup on the layer 2 switch network. Troubleshoot the switch and follow the technote for SRX Series Gateway Cluster Deployment in Layer 2 Network. 

  Is the interface link light GREEN for the Fabric Link on both Chassis Cluster nodes?

• Yes - Go to Step 5
• No   - Go to Step 4

  Change the cable that you are using for the Fabric Link. Is the interface link light GREEN?

• Yes - Previous cable was faulty. Reboot both the Chassis Cluster nodes simultaneously to get out of bad state. Does the Fabric Link come up after the reboot? If no, then continue to Step 5.
• No   - Go to Step 7

  Reconfigure the Fabric Link port to a different port of the SRX device, move the cable, and reboot the secondary node. Is the Fabric Link up now?

• Yes - Possible hardware issue with the IOC/PIM or physical port. Continue to Step 6.
• No   - Continue to Step 8.

Recommend to check the interface statistics (root@J-SRX>show interfaces <interface_name>) and open a case with your technical support representative to verify hardware issue.
Go to step 8.

  If the Fabric Link is SFP/XFP-type port, change the transceivers on both ends. Ensure that the transceivers are same type (LX, SX, etc.) and that they are Juniper-branded parts. Does this resolve the issue?

• Yes - Possible faulty transceiver  issue. Open a case with your technical support representative to resolve the hardware issue - Proceed to Step 8
  
• No   - Continue to troubleshoot this issue with technical support representative by proceeding to Step 8.

  Follow steps in KB21781 - [SRX] Data Collection Reference Checklist - Logs/data to collect for troubleshooting and open a case with your technical support representative.

show chassis cluster status
show chassis cluster statistics
show chassis cluster information
show log jsrpd
show log messages
show log chassisd
request support information