HA Live Log errors

Question

I have two clusters, both configured in active-passive mode using eth8 for ha, on the most recent firmware and no backup interface defined. However, one of the clusters has this error repeating in the logs: 
 
 2016:06:03-16:04:12 sophoswp-1 ha_daemon[4235]: id="38A2" severity="error" sys="System" sub="ha" seq="M: 130 12.295" name="send_backup_heartbeat(): send(): Network is down" 
 
 In the web interface, everything looks good. Master is Active and Slave is Ready. Physically, the link lights are up and activity lights are blinking. The error was occurring before the last firmware update and persisted after the update. Both nodes updated successfully. Since this is a production system, I am a bit hesitant to just unplug the ha cable until it is confirmed this is an issue and not just a problem with the logging.

BAlfson · Accepted Answer

A Backup Interface is not required, but it would prevent the problem you described from occurring. Also, it will allow you to try the following without forcing a fail over. 
 If that's Sophos hardware, I would have your reseller submit a ticket to Sophos Support. In the meantime, try changing that cross-over cable for eth8 and then remove the Backup Interface setting. If the log shows the the problem continues, try the same process using a different interface for syncing. By the time Support gets to you, the problem may be resolved. 
 Cheers - Bob