ECMP
Equal Cost Multiple Path (ECMP) processing is a networking feature that enables the firewall to use up to four equal-cost routes to the same destination. Without this feature, if there are multiple equal-cost routes to the same destination, the virtual router chooses one of those routes from the routing table and adds it to its forwarding table; it will not use any of the other routes unless there is an outage in the chosen route.
Enabling ECMP functionality on a virtual router allows the firewall to have up to four equal-cost paths to a destination in its forwarding table, allowing the firewall to:
Load balance flows (sessions) to the same destination over multiple equal-cost links. Efficiently use all available bandwidth on links to the same destination rather than leave some links unused. Dynamically shift traffic to another ECMP member to the same destination if a link fails, rather than having to wait for the routing protocol or RIB table to elect an alternative path/route. This can help reduce downtime when links fail.
For information about ECMP path selection when an HA peer fails, see ECMP in Active/Active HA Mode.
The following sections describe ECMP and how to configure it.

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