Fortinet FortiGate Series Administration Manual page 345

Router Static
ECMP routing of simultaneous sessions to the same destination IP
address
FortiGate Version 4.0 MR1 Administration Guide
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Weighted (also The FortiGate unit load balances sessions among ECMP routes based on
weights added to ECMP routes. More traffic is directed to routes with higher
called
weights.
weight-based)
After selecting weight-based you must add weights to static routes. See
"Configuring weighted static route load balancing" on page
Spill-over (also The FortiGate unit distributes sessions among ECMP routes based on how busy
the FortiGate interfaces added to the routes are.
called
After selecting spill-over you add route Spillover Thresholds to interfaces added
usage-based)
to ECMP routes. The FortiGate unit sends all ECMP-routed sessions to the
lowest numbered interface until the bandwidth being processed by this interface
reaches its spillover threshold. The FortiGate unit then spills additional sessions
over to the next lowest numbered interface.
The Spillover Thresholds range is 0-2097000 KBps.
For more information, including the order in which interfaces are selected, see
"Configuring spill-over or usage-based ECMP" on page
You can configure only one of these ECMP route failover and load balancing methods in a
single VDOM. If your FortiGate unit is configured for multiple VDOM operation, each
VDOM can have its own ECMP route failover and load balancing configuration.
To configure the ECMP route failover and load balancing method from the
web-based manager
1 Go to Router > Static > Static Route.
2 Set ECMP Route failover & Load Balance Method to source based, weighted, or
spill-over.
3 Select Apply.
Figure 181: Configuring ECMP route failover and load balancing method
To configure the ECMP route failover and load balancing method from the CLI
1 Enter the following command:
config system settings
set v4-ecmp-mode {source-ip-based | usage-based |
weight-based}
end
When the FortiGate unit selects an ECMP route for a session, a route cache is created
that matches the route with the destination IP address of the session. All new sessions to
the same destination IP address use the same route until the route is flushed from the
cache. Routes are flushed from the cache after a period of time when no new sessions to
the destination IP address are received.
The route cache improves FortiGate routing performance by reducing how often the
FortiGate unit looks up routes in the routing table.
If the FortiGate unit receives a large number of sessions with the same destination IP
address, because all of these sessions will be processed by the same route, it may appear
that sessions are not distributed according to the ECMP route failover and load balancing
configuration.
ECMP route failover and load balancing
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