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Syslog message: HOST LOOPBACK WEDGE DETECTED

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Article ID: KB32168 KB Last Updated: 12 Oct 2021Version: 2.0
Summary:

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 - Index of Articles for Troubleshooting PFE ASIC Syslog Events.

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Symptoms:

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

 

Cause:

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.

Solution:

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.

    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 "HOST LOOPBACK WEDGE DETECTED" message. Frequently these events help identify the cause.

This article is indexed in KB31893 - primary Index of Articles for Troubleshooting PFE ASIC Syslog Events; tag EACHIPTSG XLCHIPTSG LUCHIPTSG MQCHIPTSG


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.

 

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