Advertising preferred Hub

In this section, we advertise the preferred entry point into our SD-WAN network to the outside world. The example below makes sure that the Hub H1 is preferred by the incoming traffic if (and only if) at least one of its overlays is healthy.

This topic includes reference configurations for the following components:

• Spoke

• Hub

Spoke

1. In the SD-WAN configuration, configure the SD-WAN Neighbor feature, declaring each Hub healthy if (and only if) at least one of its overlays is healthy:

       config system sdwan
         config neighbor
           edit 10.200.1.253
             set member 2 3
             set health-check "HUB"
             set sla-id 1
             set minimum-sla-meet-members 1
           next
           edit 10.200.1.254
             set member 4 5
             set health-check "HUB"
             set sla-id 1
             set minimum-sla-meet-members 1
           next
         end
       end

2. Apply a custom BGP community when advertising to a healthy Hub:

       config router route-map
         edit "SLA_OK"
           config rule
             edit 1
               set set-community "65001:99"
             next
           end
         next
       end
       config router bgp
         config neighbor
           edit 10.200.1.253
             set route-map-out-preferable "SLA_OK"
           next
           edit 10.200.1.254
             set route-map-out-preferable "SLA_OK"
           next
       end

When using segmentation over a single overlay, the command route-map-out-vpnv4-preferable must be used instead of route-map-out-preferable.

Hub

1. Define the custom BGP community sent by the Spokes:

       config router community-list
         edit "SLA_OK"
           config rule
             edit 1
               set action permit
               set match "65001:99"
             next
           end
         next
       end

2. When advertising SD-WAN routes to external peers, match on the above community, and set BGP attributes accordingly, to guarantee that the traffic is attracted as desired.

   For example, if the desired behavior is to prefer the Hub H1 if (and only if) at least one of its overlays is healthy, then we can use BGP MED attribute and ensure that:

   • Whenever H1 is healthy, it is preferred.
   • Whenever H1 is not healthy, but H2 is healthy, then H2 is preferred.

   Assuming that the external peer's IP is 192.168.1.1, the following snippets will achieve the desired result:

   On Hub H1:

       config router route-map
         edit “H1_TO_OUTSIDE”
           config rule
             edit 1
               set match-community “SLA_OK”
               set set-metric 90
             next
             edit 2
               set set-metric 100
             next
           end
         next
       end
       config router bgp
         config neighbor
           edit “192.168.1.1”
             set route-map-out “H1_TO_OUTSIDE”
           next
         end
       end

   On Hub H2:

       config router route-map
         edit “H2_TO_OUTSIDE”
           config rule
             edit 1
               set match-community “SLA_OK”
               set set-metric 95
             next
             edit 2
               set set-metric 105
             next
           end
         next
       end
       config router bgp
         config neighbor
           edit “192.168.1.1”
             set route-map-out “H2_TO_OUTSIDE”
           next
         end
       end