The "FI Link sanity checks" message reports a transient hardware issue.

When a "FI Link sanity checks" event occurs, a message similar to the following is reported:

Jan 22 175942 router0 %PFE-3 fpc0 XMCHIP(2)XMCHIP(2) FI Link sanity checks - Type 4 Seq Number 1983 Stream 7 Link0 0x80 Link1 0x60 Link2 0x8001

1. Traffic impact depends on the counter value and the frequency. Each counter is a cell drop and Link Sanity check event will have a very brief (few msec) traffic interruption for the PFE reporting.
2. If this event happens several times in sequence there might an exposure. Traffic flows passing from the fabric side for this PFE entity might experience higher latency up to 500msec, without traffic drop and restarting the FPC is strongly recommended
3. This is minor alarm as single event does not cause permanent operational impact. A major alarm will be reported when seen with  KB31611 - Syslog message: XMCHIP.*FI.*Cell underflow at the state stage [juniper.net] .

This issue may be caused by hardware transient errors. A complete software workaround or fix is not available. Enhancements have been added in PR1264656 and PR1262868 to check the combination of Link Sanity checks interrupt and cell underflow events and verify there is true operational impact to report a new event, such as the following syslog entries.

• FI: Link sanity check and high rate cell underflow errors
• FI: Cell underflow errors with reorder engine pointers stalled

{DIDYOUKNOWSERVICENOWTOKEN.EN_US}

Perform these steps to determine the cause and resolve the problem (if any).  Continue through each step until the problem is resolved.

1. Collect the show command output.

   {SYSLOGSERVICENOWTOKEN.EN_US}

   Capture the output to a file (in case you have to open a technical support case). To do this, configure each SSH client/terminal emulator to log your session.

   show log messages
show log chassisd
start shell network pfe <fpc#>
show nvram
show syslog messages
exit

2. Analyze the show command output.

   In the 'show log messages', review the events that occurred at or just before the appearance of the "FI Link sanity checks" message. Frequently these events help identify the cause.

   • No RMA required.
   • Restart the MPC and monitor the errors.
   • Contact your technical support representative if the issue is seen after a FPC restart.

This article is indexed in  KB31893 - Primary Index of Articles for Troubleshooting PFE ASIC Syslog Events [juniper.net] ; tag XMCHIPTSG

Tip: When looking at an event in the logs, it is important to focus on the first error message in a collection of syslog messages. The first error message is usually the cause of all the follow-on error messages. The follow-on collateral damage error messages can be ignored.

• PR1264656 - All traffic is dropped with cell underflow due to fabric stream wedge
• PR1262868 - raise major CMERROR alarm upon combination of Links Sanity Interrupt and Cell underflow drops