The "HOST LOOPBACK WEDGE DETECTED" message is caused due to packet forwarding readiness from WAN interfaces to the Host got compromised 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] . .
When a "HOST LOOPBACK WEDGE DETECTED" event occurs messages similar of the following are reported:
Mar 30 14:31:13.276 atlas-re0 fpc4 Host Loopback:HOST LOOPBACK WEDGE DETECTED IN PATH ID 1 Mar 30 14:31:13.373 atlas-re0 fpc4 Host Loopback:HOST LOOPBACK WEDGE DETECTED IN PATH ID 2
Indications:
PFE wedge of the WAN forwarding block/circuit is detected and traffic forwarding is compromised
Major Alarm will be raised
The host-path from the WAN interfaces is always validated by periodic host loopback probes. If this forwarding path healthiness validation fails for 10 seconds, a major alarm is raised. In the majority of all events, this is a post effect of some other hardware or software related errors compromising packet forwarding. Other syslog events need to be examined to come to the trigger of such host loopback wedge conditions.
Perform these steps to determine the cause and resolve the problem (if any). Continue through each step until the problem is resolved.
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.
show log messages show log chassisd start shell network pfe <fpc#> show nvram show syslog messages exit
Analyze the show command output.
In the 'show log messages', review the events that occurred at or just before the appearance of the "HOST LOOPBACK WEDGE DETECTED" message. Frequently these events help identify the cause.
No RMA required.
Look for pfe_debug files or ttraces under /var/tmp directory and collect additional data with the script before FPC restart is performed KB31922 - shell script collecting data if packet forwarding at Packet Forwarding Engine is compromised [juniper.net] to be uploaded for further investigations with your technical support representative.
Junos OS software changes are made within PR1172409 to avoid host looback probes getting behind.
The generic pfe-disable event script will detect the wedge condition that happens as a result of this event and invoke the pfe-disable action; see KB31867 - Generic pfe-disable Event Script [juniper.net] . A FPC restart at a later time is needed to bring the PFE back into service.
Perform FPC restart to recover if such an event is reported together with other hardware related 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 EACHIPTSG XLCHIPTSG LUCHIPTSG MQCHIPTSG