Merge pull request #231654 from halkazwini/rs-preference

Route Server: New release: Routing preference

Author: v-stsavell

articles/route-server/TOC.yml

@@ -37,6 +37,8 @@
     href: about-dual-homed-network.md
   - name: Path selection
     href: path-selection.md
+  - name: Routing preference
+    href: routing-preference.md
   - name: Multi-region design
     href: multiregion.md
   - name: Injecting routes to AVS

articles/route-server/routing-preference.md

@@ -0,0 +1,35 @@
+---
+title: Routing preference
+titleSuffix: Azure Route Server
+description: Learn about Azure Route Server routing preference feature. 
+author: halkazwini
+ms.author: halkazwini
+ms.service: route-server
+ms.topic: conceptual
+ms.date: 03/28/2023
+ms.custom: template-concept
+---
+
+# Azure Route Server routing preference
+
+Azure Route Server enables dynamic routing between network virtual appliances (NVAs) and virtual networks (VNets). In addition to supporting third-party NVAs, Route Server also seamlessly integrates with ExpressRoute and VPN gateways. Route Server uses built-in route selection algorithms to make routing decisions to set connection preferences.
+
+When **branch-to-branch** is enabled and Route Server learns multiple routes across site-to-site (S2S) VPN, ExpressRoute and SD-WAN NVAs, for the same on-premises destination route prefix, users can now configure connection preferences to influence Route Server route selection.
+
+## Routing preference configuration
+
+When Route Server has multiple routes to an on-premises destination prefix, Route Server selects the best route(s) in order of preference, as follows:
+
+1. Prefer routes with the longest prefix match (LPM)
+1. Prefer static routes over BGP routes
+1. Prefer routes based on routing preference configuration:
+    * **ExpressRoute**: (This is the default setting): Prefer routes learned through ExpressRoute over routes learned through VPN/SD-WAN connections
+    * **VPN/SD-WAN**: Prefer routes learned through VPN/SD-WAN connections over routes learned through ExpressRoute.
+    > [!IMPORTANT]
+    > Routing preference doesn't allow users to set preference between routes learned over VPN and SD-WAN connections. If the same routes are learned over VPN and SD-WAN connections, Route Server will prefer the route with the shortest BGP AS-PATH.
+    * **AS-Path**: Prefer routes with the shortest BGP AS-PATH length, irrespective of the source of the route advertisement. 
+
+## Next steps
+
+- Learn how to [configure Azure Route Server](quickstart-configure-route-server-portal.md).
+- Learn how to [monitor Azure Route Server](monitor-route-server.md).