Fortinet FortiGate FortiGate-5000 Backplane Communications Manual page 20

HA configurations
20
Choosing the slot position
Depending on the types of communications, HA or other, that you want to pass
through your FortiSwitch modules, you may choose to install FortiSwitch-5003
modules in different slots: slot 1, slot 2, or both. (Other hardware configurations
are possible but often not preferable for various reasons, such as points of failure
or base backplane topology.)
When using FortiSwitch modules to provide a network connection to the base
backplane, slot position does not matter. However, you can improve robustness
by installing FortiSwitch modules in both slots and providing a redundant link.
For all types of communication, using both slots has the advantage of improving
reliability of communications through or to the base backplane because no
FortiSwitch is a single point of failure. Using both slots also provides the option of
separating multiple sensitive or high volume communications, such as HA
communications for multiple clusters.
Note: For HA configurations, you can further improve fault tolerance by adding one or more
non-base backplane interfaces as heartbeat interface failovers.
However, if you install only one FortiSwitch module, in addition to fault tolerance
considerations, the slot position has additional effects specific to HA.
• Inter-chassis HA configurations require that the switch use the same slot
number in each chassis so that each cluster member's configuration uses the
same heartbeat interface.
• Slot position affects HA heartbeat interface selection and failover order.
Slot position and HA heartbeat interface precedence
When installing only one FortiSwitch-5003 module with an HA cluster of
FortiGate-5001SX or FortiGate-5001FA2 modules, it is usually preferable to use
slot 2. This allows you to connect one or more of the other FortiGate-5001SX or
FortiGate-5001FA2 interfaces as backup HA heartbeat interfaces.
The preferred FortiSwitch module slot is different for FortiGate-5005FA2 module
HA clusters. In this case, it is usually preferable to use slot 1.
The reason for selecting different slots is related to the mechanism for heartbeat
interface selection, which is indirectly tied to slot number.
During heartbeat interface selection, the heartbeat interface with the highest
priority is selected first. If multiple heartbeat interfaces have highest priority,
including when all have equal priority, the HA cluster chooses a heartbeat
interface using the Heartbeat Interface list.
This list is sorted into hash map order, rather than purely by alphabetical order or
purely by interface number value comparisons. As a result, the list is sorted
primarily alphabetical by interface name (for example, base1 is before port1), then
secondarily by index numbers:
• 1
• 10
• 2 through 8
• 9
FortiGate-5000 Series Version 3.0 MR5 Backplane Communications Guide
FortiGate-5140 base backplane communication
01-30005-0423-20070829