HA Active-Active issues with software-switch ports

[AnotherFortiUser]

Hi, we have two FortiGateRugged 60F in an active-active HA cluster.
internal1 and internal2 ports were originally members of a hardware switch interface, with 5 VLANs.

We changed the configuration to a software switch interface, to have a more granular control over the vlans for the seperate two ports, because the first approach doesn't allow to assign some VLANs on internal1, and some other (but overlapping) VLANs on internal2.

The problem: Prior to the change from hardware switch to software switch, we could unplug the cable on port internal2 on FortiGate A (Primary, higher priority) and the traffic would be forwarded through internal2 on FortiGate B.
But this isnt possible anymore. If we unplug the cable, there is no rerouting/forwarding and the connection is simply lost. I guess the FortiGate cluster still keeps FortiGate A as Primary, even though one interface is down?

I wanted to add the two interfaces to the "monitored interfaces" of the HA, but this isnt possible - apparently due to using the software switch type. But in the earlier setup with the hardware switch, there weren't any interfaces monitored as well...? I confirmed this by looking in the older configuration file.

How can this be possible? Does traffic of a down interface get forwarded to the secondary FortiGate without the FortiGates in an HA changing their primary/secondary status?
Is this even possible with a software switch? When I searched online, I found multiple sources stating that software switch / VLANs interfaces cannot be monitored..

Thank you in advance!

[sjoshi]

When using a software switch interface with VLANs on FortiGate devices in an active-active HA cluster, the behavior you described is expected. In this setup, unplugging a cable from one interface will not trigger automatic failover to the secondary FortiGate as it did with the hardware switch configuration. The HA cluster will still consider the primary FortiGate as active even if one interface is down. Unfortunately, monitored interfaces cannot be configured with a software switch type, which explains why you cannot add them to the monitored interfaces list. In this case, manual intervention may be required to reroute traffic in the event of an interface failure since automatic failover is not supported with software switch interfaces in an active-active HA cluster configuration.

[AnotherFortiUser]

Thank you all for your replies. So the reason for the issue is as I suspected: The "problem" is the software switch interface type.

The solution would be to change it back to hardware switch, which would allow us to monitor the interface and get the HA working again.
However, we needed to use the software switch functionality specifically, because we had another issue..just as a short summary: The hardware switch type wouldn't allow to have overlapping / different vlans assigned to specific ports. To be precise:
We need to have two trunk ports on internal1 and internal2. internal1 should have the VLANs 1, 2 and 3. And internal2 should only have the VLANs 1 and 2.

We got this to work only with the software switch type, which allows the additional assignment per port of specific VLANs, that are not shared among the switch interface members.
(Software Switch interface with members internal1 and internal2: VLANs 1 and 2. Additionally, internal1 gets assigned VLAN 3).

But if the software switch type cannot be monitored, we need to think of a different solution - because the availability is more important. Maybe we change the network behind port internal2 to a completely different subnet/VLAN...or change something in the network topology... :\

Anyway, thank you already for your fast responses and support! :)

[AnotherFortiUser]

Just to confirm: I just added a hardware switch interface and assigned an available port to it. Yet I am still not able to monitor either the hardware switch or the member port of it. (they don't appear in the list of interfaces, when I try to add interface monitors in the HA configuration).

Is there a failover, as you described, that automatically triggers if one interface of a hardware switch goes down - even though these ports are not actively monitored or in the list of monitored interfaces in the HA configuration?

[callmeahero]

HA Behavior with Software Switches: When using a software switch, the FortiGate units can't monitor individual interfaces within that switch for HA purposes.

In your original setup (hardware switch), both interfaces were likely part of the same HA group, and failover worked as expected.

But with the software switch, HA doesn't see each interface separately, so it doesn’t trigger failover when one interface goes down.

Why the Traffic is Lost: Since the software switch combines the interfaces into a single logical interface, HA doesn't monitor each individual port.

So, if you unplug the cable from internal2 on FortiGate A, it doesn’t trigger failover, and FortiGate B doesn't take over automatically because it's not aware that the interface went down.

How to Fix It: To make failover work again, you could: Revert to using a hardware switch for these interfaces if you want HA to monitor the interfaces separately.

Or, if you stick with the software switch, you might need to configure link monitoring at the software switch level, but keep in mind that this won’t be the same as monitoring individual interfaces.

Why No Interfaces Were Monitored Before: In the hardware switch setup, the system might have monitored the entire switch interface (not individual ports), which would explain why no specific interfaces were listed as "monitored" in your HA config.

[AnotherFortiUser]

Thank you as well for your response and help!
I already answered the common points in the above reply, but in addition to your comment:
Link monitoring sadly wont be an option, because we do not have another "reliable" device in this network, that can be considered for constantly monitoring the connection/availability. In other words: If the connection to a specific device/host inside our network is lost, the FortiGate shouldnt switch primary/secondary status.

[callmeahero]

Hope it helps.