Configuring Hub devices

The second part of the solution is to configure the Hub, so that it makes use of the information signaled by the Edge.

Create (or import) a new CLI Template, called 04-Hub-Signal-SLA:

config router community-list

edit "SLA_OK"

config rule

edit 1

set action permit

set match "$(as):99"

next

end

next

end

config router route-map

edit "EDGE_IN"

config rule

edit 1

set match-community "SLA_OK"

set set-route-tag 99

next

edit 100

next

end

next

end

config router bgp

config neighbor-group

edit "EDGE"

set route-map-in "EDGE_IN"

next

end

end

This CLI Template defines the same custom BGP Community on the Hub side and uses a new route-map EDGE_IN to assign a custom route-tag (99 in our example) to the routes with that Community attached. This route-map is applied as route-map-in to all the routes learned from the Edge devices.

As a result, all the routes learned via healthy overlays will be assigned the route tag 99 (in our example).

Add the new CLI template to the group Hub-Template applied to the Hub:

One common idea is to apply a higher local-preference (or weight) to the routes marked with SLA_OK community, so that BGP on the Hub prefers them over the routes via unhealthy overlays. While this approach would work in a basic case, we do not recommend it. Recall that in the SD-WAN solution, the duty to steer the traffic must be delegated to SD-WAN! We would like BGP to keep all available routes and let SD-WAN select the preferred path for each case. For example, certain non-business-critical traffic might be still steered via an unhealthy (but cheaper) overlay. Whether it is Edge-to-Hub or Hub-to-Edge traffic, it requires a valid route on the Hub via the unhealthy overlay. Giving this route lower local-preference (or weight) would remove it from the routing table, thus violating this requirement.

We will now configure SD-WAN Rules on the Hub that will prefer the healthy overlays, based on the route tags:

• Edit the SD-WAN Template Hub-Template (assigned to the Hub).
• Create an SD-WAN Rule called INET_OK, matching the Route Tag as Destination and explicitly specifying the EDGE_INET member for it (using Manual strategy):

  

• Similarly, create another SD-WAN Rule called MPLS_OK, matching the same Route Tag as Destination and explicitly specifying the EDGE_MPLS member for it (using Manual strategy):

  

Save the changes and install the configuration on the Hub by using the Quick Install (Device DB) method.