The "FO Request timeout error" message reports a transient or permanent Hardware issue since the cell is dropped

Generally the Packet Forwarding Engines (PFEs) send traffic to another PFE using high-speed links (HSLs). When the fabric has traffic destined to another PFE/FPC, it sends out a fabric request to the destination hardware asking for permission or bandwidth to pass the traffic to the destination and waits for the reply.

Sometimes there will not be any response from the destination hardware due to some error conditions either on the source hardware or the destination in which case the source PFE will report "FO: Request timeout error".

The "FO: Request timeout error" is not necessary an indication that there is any error with the FPC reporting the error and needs to be investigated.

When an "FO Request timeout error" event occurs, a message similar to the following is reported:

Jun 9 16:19:16 router0 fpc0 XMCHIP(1): FO: Request timeout error - Number of timeouts 1, RC select 1, Stream 8
 

Indications:

• Single occurrence of syslog, not seen with other events, indicates one time transient error. No impact is expected.
• Multiple continuous occurrences indicate persistent underlying issues and needs investigation.
• Traffic impact or permanent impact on packet forwarding may happen if errors are reported repeated.

This is due to a transient hardware issue internal to the XMCHIP FO section. A minor alarm will be reported if the error rate is > 100/second.

If it only occurs once or a few times, then most likely the message is due to transient link errors on the hardware. No impact is expected.

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.
    

   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.
    

   From RE CLI
   >show chassis alarms
   >show chassis fpc
   >show chassis fabric summary
   >show chassis fabric fpcs
   >show chassis fabric plane
   >show chassis fabric plane-location
   >show chassis fabric destinations
   >show log messages
   >show log chassisd
   >show class-of-service fabric statistics
    
   From PFE shell
   >start shell pfe network fpc<fpc-number>
   #show syslog messages
   #show nvram
   #show cmerror module
   #show hsl2 statistics
   #show pfe statistics traffic
   #show pfe statistics errors
   #show xmchip <pfe-id> fo stats
    

2. Analyze the show command output.

In the 'show log messages', review the events that occurred at or just before the appearance of the "FO: Request timeout error" message. Frequently, these events help identify the cause.
 

• No RMA required.
• Contact your technical support representative​ if rate is >100/second to investigate further

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.

2021-10-11: Updated title of linked KB.
2019-10-14: Article reviewed for accuracy; no changes required.