Merge pull request #259658 from duongau/erecmp

ExpressRoute FAQ - Update note about ECMP

Author: prmerger-automator[bot]

articles/expressroute/expressroute-faqs.md

@@ -5,7 +5,7 @@ services: expressroute
 author: duongau
 ms.service: expressroute
 ms.topic: conceptual
-ms.date: 06/12/2023
+ms.date: 11/28/2023
 ms.author: duau
 
 ---
@@ -186,7 +186,8 @@ See [here](./designing-for-high-availability-with-expressroute.md) for designing
 You can achieve high availability by connecting up to 4 ExpressRoute circuits in the same peering location to your virtual network. You can also connect up to 16 ExpressRoute circuits in different peering locations to your virtual network. For example, Singapore and Singapore2. If one ExpressRoute circuit disconnects, connectivity fails over to another ExpressRoute circuit. By default, traffic leaving your virtual network is routed based on Equal Cost Multi-path Routing (ECMP). You can use **connection weight** to prefer one circuit to another. For more information, see [Optimizing ExpressRoute Routing](expressroute-optimize-routing.md).
 
 > [!NOTE]
-> Although it is possible to connect up to 16 circuits to your virtual network, the outgoing traffic from your virtual network will be load-balanced using Equal-Cost Multipath (ECMP) across a maximum of 4 circuits.
+> - Although it is possible to connect up to 16 circuits to your virtual network, the outgoing traffic from your virtual network will be load-balanced using Equal-Cost Multipath (ECMP) across a maximum of 4 circuits.
+> - Equal-Cost Multipath (ECMP) in ExpressRoute uses the Per-Flow (based on 5-tuple) load balancing method. Accordingly, traffic flow between a given source and destination host pair are guaranteed to take the same path, even if multiple ECMP paths are available. 
 
 ### How do I ensure that my traffic destined for Azure Public services like Azure Storage and Azure SQL on Microsoft peering or public peering is preferred on the ExpressRoute path?