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When multiple BGP neighbors must be configured, administrators may streamline the process by creating BGP neighbor groups and neighbor-range commands.
As an example:
config router bgp
set as Y.Y.Y.Y
set router-id z.z.z.z
set holdtime-timer 60
set ebgp-multipath enable
set ibgp-multipath enable
set additional-path enable
set graceful-restart enable
next
end
config neighbor-group
edit "test_1"
set capability-graceful-restart enable
set link-down-failover enable
set next-hop-self enable
set soft-reconfiguration enable
set remote-as X.X.X.X
next
end
config neighbor-range
edit 1
set prefix 192.10.10.0 255.255.255.0
set neighbor-group "test_1"
next
end
Administrators typically also enable the Graceful Restart feature to prevent network disruptions and packet loss during an HA failover or when the primary FortiGate in an HA cluster is rebooted.
When using a BGP neighbor-group is used, packet loss may occur during failover testing.
Reverting the configuration to manually configured neighbors eliminates the packet loss, indicating a potential issue with Graceful Restart when using BGP neighbor-group and neighbor-range commands.
Conclusion:
Since neighbor-groups are passive and cannot trigger a re-connection, it is expected that neighbor-groups defined with neighbor-range cannot perform Graceful Restart when it is the side that initiates a restart.
BGP graceful restart against dynamic BGP peers during a HA failover is not supported at this time in FortiOS.
To prevent packet loss using BGP neighbor-groups on SD-WAN Hubs, each spoke must activate the route-stale option on BGP neighborship with each Hub:
config router bgp
config neighbor
edit Y.Y.Y.Y
set stale-route enable
next
end
Instead, in order to benefit fully from the Grace Restart feature, BGP configuration would need to be modified to manually configure neighbors instead of neighbor-groups defined with neighbor-range.
Related articles:
Technical Tip: Configuring FortiGate HA and BGP graceful-restart to avoid traffic interruption durin...
Technical Tip: Understanding Graceful restart and non-stop forwarding for BGP in FortiGate HA
Technical Tip: Understanding Graceful restart and non-stop forwarding for OSPF in FortiGate HA
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