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In some cases, when administrators need to configure multiple BGP neighbors, to simplify the configuration, BGP neighbor groups are created and defined with the neighbor-range command.
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 usually also want to use the Graceful Restart feature to avoid network disruptions and packet loss in cases of a failover or a reboot of the cluster.
How BGP graceful restart works in that scenario is explained here: Understanding Graceful restart and non-stop forwarding for BGP in FortiGate HA
When using this 'neighbor-groups', during failover testing, packet loss can be seen.
Reverting the configuration to manually configured neighbors corrects the packet loss. This indicates a possible issue with Graceful Restart when using BGP neighbor groups defined with the neighbor-range command.
Conclusion:
Since neighbor-groups are passive and cannot trigger a re-connection, it's expected that neighbor-groups defined with neighbor-range can't 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 avoid packet loss using BGP neighbor-groups on SD-WAN Hubs, it is necessary to activate the route-stale option on each BGP neighborship with each Hub on every Spoke:
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.
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