Fortinet 5003A Benutzerhandbuch

The configuration of the spanning tree instances determines whether you create 
an active-passive or active-active configuration:

• For an active-passive configuration, you can create one spanning tree 

instance on all three devices and give one of the FortiSwitch-5003A boards a 
higher priority. This board becomes the active board in the configuration 
because spanning tree sends all traffic to the high priority spanning tree 
instance. If the active board fails, spanning tree re-directs all traffic to the other 
board.

• For an active-active configuration, you create two or more spanning tree 

instances on all three devices and give some instances a higher priority on one 
FortiSwitch-5003A board and give other instances a higher on the other 
FortiSwitch-5003A board. While both FortiSwitch-5003A boards are, the 
spanning tree configuration distributes traffic to both boards. If one of the 
FortiSwitch-5003A boards fails, spanning tree redirects all of the traffic to the 
board that is still operating.

In both active-passive or active-active configurations, if one of the 
FortiSwitch-5003A boards fails, sessions are temporarily interrupted because the 
FortiSwitch-5003A boards do not store session information.

 shows an example redundant link aggregation configuration. In this 

configuration an external switch is connected to two FortiSwitch-5003A front panel 
F7 interfaces. The switch adds VLAN tags to traffic from two internal and two 
external networks. Packets from each network get different VLAN tags. Packets 
from internal networks are tagged as 103 and 104 and packets from the external 
networks are tagged as 105 and 106.

To make this an active-passive configuration, the spanning tree instances on the 
FortiSwitch-5003A board in slot 1 should have a higher priority than the spanning 
tree instances on the FortiSwitch-5003A board in slot 2. The FortiSwitch-5003A 
board in slot 1 becomes the root for both spanning tree instances. Because of the 
priority settings, MSTP sends all packets to the FortiSwitch-5003A board in slot 1. 
If this board fails, MSTP re-directs all packets to the FortiSwitch-5003A board in 
slot 2. 

For a given spanning tree instance, MSTP directs packets to the device with the 
lowest priority value. To give a spanning tree instance a higher priority on a device 
you must configure the instance on that device with a lower priority value. The 
lower priority value gives the device a higher spanning tree priority for a given 
spanning tree instance. 

In this example the spanning tree priority values on the FortiSwitch-5003A board 
in slot 1 are both set to 4096 and the spanning tree priority values on the 
FortiSwitch-5003A board in slot 2 are both set to 40960. So spanning tree directs 
all traffic to the FortiSwitch-5003A board in slot 1.

Note: If you have more than one spanning tree instance you can still configure an 
active-passive configuration by setting the priorities of all spanning tree instances to be 
higher for the same FortiSwitch-5003A board.