For SD-WAN, there are two main types of routes:
Local Routes: Any route that an SD-WAN Edge learns locally. This could be a connected subnet, a statically configured route, or any route that is learned through BGP or OSPF.
Remote Routes: Routes that are learned via VCRP are referred to as remote routes. To put it another way, a route that is not locally present on an Edge is considered to be a remote route. Depending on the configuration, this route was originating from a different Edge, and it is transmitted by the Gateway to other Edges inside the customer enterprise.
When it comes to non-dynamic routes (BGP and OSPF) that are unchangeable, SD-WAN routes traffic in a rigid order. Nonetheless, in certain situations, you can control the routing flow by applying the Longest Prefix Match method.
Ordering of routes in an edge:
- longest prefix length.
- Locally connected.
- If the preferred choice is turned on, local static will be used (LAN static < WAN static).But overlay routes will be preferred if the preferred option is not
- NSD static routes local. NSD IPsec wins over NSD GRE.
- Remote NSD static.
- Remote Edge connected.
- Remote edge LAN/WAN Static.
- PG static.PG secure static > PG non-secure static.
- Overlay Flow Control (OFC) or Distributed Cost Calculation Driven route order are two types of dynamic routes.
- It is preferable to use site local routes (OSPF Inter/Intra, BGP non-uplink) rather than routes that are extremely dynamic.
- Local OSPF routes between and within areas win over Local BGP routes.
- Local OSPF-external (OE1/OE2) is defeated by Local BGP.
- Local routes that aren’t preferred win over remote routes with preferred cost (OE1, OE2, UPLINK BGP).
- Preference is taken to be considered in the remote dynamic routes (lower preference wins).
- BGP attributes and OSPF metrics are compared if preferences are the same.
- OSPF INTRA> INTER > OE1 > OE2
- BGP
- Higher local preference
- Lower AS_PATH Length
- Smaller BGP metric
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