The "Invalid cell Sequence start without SOP" message reports a software issue in the EACHIP when packets larger than 16K bytes are being processed.

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 an "Invalid cell Sequence start without SOP" event occurs, a message similar to the following is reported:

Jul 11 13:24:57.586 router0 fpc0 Cmerror Op Set: MQSS(0): MQSS(0): BCMW ICM: Invalid cell sequence (Back-to-back SOP, Packet start without SOP or 16K packet bytes without SOP)

Indications:

• Permanent impact of packet forwarding in the PFE forwarding will be seen

• Alarm will be raised

This is due to a software issue or transient hardware issue within the EACHIP. One possible cause may be the dynamic tunnel interface application defect adding tunnel headers during route forwarding lookup loop until it reaches the 16k limit.

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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 "Invalid cell Sequence start without SOP" message. Frequently these events help identify the cause.

• No RMA is required

• Collect debugging information using  KB31922 - shell script collecting data if packet forwarding at Packet Forwarding Engine is compromised  [juniper.net]

• The generic pfe-disable event script will detect a permanent impact on packet forwarding condition that happens as a result of this event and invoke the pfe-disable action.  KB31867 - [Junos] Generic pfe-disable event script [juniper.net]

• ​ FPC restart  during a maintenance window should clear this error.

• 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

Note: KB Team - All changes to this article must be approved by the AI-Scripts Review team ( [email protected] ) before re-publishing.