Implementing route discovery with BGP

BGP allows the branch and data center FortiGates to dynamically discover routes from each other. To make this happen add the data center FortiGate IPsec VPN tunnel interface IP addresses to the branch BGP configuration as BGP peers.

Routes that have the same network mask, administrative distance, and priority are automatically considered for SD-WAN when the interfaces where those routes are learned are added to the SD-WAN interface group.

Begin by adding a route-map to set the extended tag to 10.

config router route-map

edit "add-tag"

config rule

edit 1

set set-extended_tag 10

end

The branch BGP configuration includes:

• Enabling ebgp-multipath
• Enabling soft-reconfiguration, link-down-failover, and ebgp-enforce-multihop for each BGP peer
• Adding the data center remote-as (which is 65500) to each peer configuration
• Setting the prefix for the neighbor range to the network matching the BGP peers
• Set route-map-in to the configured route-map tag (add-tag) for each BGP peer.

To facilitate the fastest route failovers, the following timers are set to their lowest values:

• scan-time
• advertisement-interval
• keep-alive timer
• holdtime-timer

config router bgp

set as 65501

set router-id 10.254.0.2

set keepalive-timer 1

set holdtime-timer 3

set ebgp-multipath enable

set scan-time 5

set distance-external 1

config neighbor

edit "10.254.0.1"

set advertisement-interval 1

set link-down-failover enable

set soft-reconfiguration enable

set remote-as 65500

set route-map-in add-tag

set ebgp-enforce-multihop enable

next

edit "10.254.1.1"

set advertisement-interval 1

set link-down-failover enable

set soft-reconfiguration enable

set remote-as 65500

set route-map-in add-tag

set ebgp-enforce-multihop enable

next

end

end