The "Unroll TAIL length overflow" message reports that the packet size used in the forwarding path at a certain stage is greater than the original packet size.

This is a Troubleshooting Article for a PFE ASIC Syslog Event.
To view other documented syslog events related to XMCHIP, XLCHIP, MQCHIP, LUCHIP, EACHIP, and PECHIP, see KB31893 - Master Index of Articles for Troubleshooting PFE ASIC Syslog Events [juniper.net] .

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When a "Unroll TAIL length overflow" event occurs, a message similar to the following is reported:

Jul 23 18:41:49.164 router: %PFE-3: fpc8 Cmerror Op Set: MQSS(0): MQSS(0): LI-0: Unroll TAIL length overflow

Indications:

• Permanent impact on packet forwarding will be seen if errors are seen

• Alarm will be raised​

This is likely due to a software micro-code error.

{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 "Unroll TAIL length overflow" message. Frequently these events help identify the cause.

• No RMA is required

• FPC restart  is needed to recover or using the using the script to disable the PFE  KB31867 - [Junos] Generic pfe-disable event script [juniper.net]

• Contact your technical support representative immediately

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

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.

2019-10-01: Article reviewed for accuracy; no changes required