Monitoring VLAN interfaces

Monitoring VLAN interfaces

If the FortiGates in the cluster have VLAN interfaces, you can use the following command to monitor all VLAN interfaces and write a log message if one of the VLAN interfaces is found to be down.

Once configured, this feature works by verifying that the primary unit can connect to the subordinate unit over each VLAN. This verifies that the switch that the VLAN interfaces are connected to is configured correctly for each VLAN. If the primary unit cannot connect to the subordinate unit over one of the configured VLANs the primary unit writes a link monitor log message indicating that the named VLAN went down (log message id 20099). Use the following CLI command to enable monitoring VLAN interfaces:

config system ha-monitor

set monitor-vlan enable/disable

set vlan-hb-interval <interval_seconds>

set vlan-hb-lost-threshold <vlan-lost-heartbeat-threshold>


vlan-hb-interval is the time between sending VLAN heartbeat packets over the VLAN. The VLAN

heartbeat range is 1 to 30 seconds. The default is 5 seconds.


vlan-hb-lost-threshold is the number of consecutive VLAN heartbeat packets that are not successfully received accross the VLAN before assuming that the VLAN is down. The default value is 3, meaning that if 3 heartbeat packets sent over the VLAN are not received then the VLAN is considered to be down. The range is 1 to 60 packets.

A VLAN heartbeat interval of 5 means the time between heartbeat packets is five seconds. A VLAN heartbeat threshold of 3 means it takes 5 x 3 = 15 seconds to detect that a VLAN is down.

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About Mike

Michael Pruett, CISSP has a wide range of cyber-security and network engineering expertise. The plethora of vendors that resell hardware but have zero engineering knowledge resulting in the wrong hardware or configuration being deployed is a major pet peeve of Michael's. This site was started in an effort to spread information while providing the option of quality consulting services at a much lower price than Fortinet Professional Services. Owns PacketLlama.Com (Fortinet Hardware Sales) and Office Of The CISO, LLC (Cybersecurity consulting firm).

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