Update gateway-migration.md

Update with Common Validation Scenarios

Author: mialdrid

articles/expressroute/gateway-migration.md

@@ -13,7 +13,7 @@ ms.author: duau
 
 # Migrate to an availability zone-enabled ExpressRoute virtual network gateway (Preview)
 
-A virtual network gateway requires a gateway SKU that determines its performance and capacity. Higher gateway SKUs provide more CPUs and network bandwidth for the gateway, enabling faster and more reliable network connections to the virtual network.
+When you create an ExpressRoute virtual network gateway, you need to specify the gateway SKU that you want to use. When you select a higher gateway SKU, more CPUs and network bandwidth are allocated to the gateway, and as a result, the gateway can support higher network throughput and more dependable network connections to the virtual network. 
 
 The following SKUs are available for ExpressRoute virtual network gateways:
 
@@ -23,50 +23,44 @@ The following SKUs are available for ExpressRoute virtual network gateways:
 * ErGw1Az
 * ErGw2Az
 * ErGw3Az
+* ErGwScale (Preview)
 
-## Supported migration scenarios
-
-To increase the performance and capacity of your gateway, you have two options: use the `Resize-AzVirtualNetworkGateway` PowerShell cmdlet or upgrade the gateway SKU in the Azure portal. The following upgrades are supported:
-
-* Standard to HighPerformance
-* Standard to UltraPerformance
-* ErGw1Az to ErGw2Az
-* ErGw1Az to ErGw3Az
-* ErGw2Az to ErGw3Az
-* Default to Standard
-
-You can also reduce the capacity and performance of your gateway by choosing a lower gateway SKU. The supported downgrades are:
-
-* HighPerformance to Standard
-* ErGw2Az to ErGw1Az
-
-## Availability zones
+## Availability zone enabled SKUs
+The ErGw1Az, ErGw2Az, ErGw3Az and ErGwScale (Preview) SKUs, also known as Az-Enabled SKUs, support Availability zone deployments. This feature provides high availability and resiliency to the gateway by distributing the gateway across multiple availability zones.  
 
-The ErGw1Az, ErGw2Az, ErGw3Az and ErGwScale (Preview) SKUs, also known as Az-Enabled SKUs, support [Availability Zone deployments](../reliability/availability-zones-overview.md). The Standard, HighPerformance and UltraPerformance SKUs, also known as Non-Az-Enabled SKUs, don't support this feature.
+The Standard, HighPerformance, and UltraPerformance SKUs, which are also known as non-availability zone enabled SKUs are historically associated with Basic IPs, do not support the distribution of the gateway across multiple availability zones.  
 
-> [!NOTE]
-> For optimal reliability, Azure suggests using an Az-Enabled virtual network gateway SKU with a [zone-redundant configuration](../reliability/availability-zones-overview.md#zonal-and-zone-redundant-services), which distributes the gateway across multiple availability zones.
->
+For enhanced reliability, it is recommended to use an Availability-Zone Enabled virtual network gateway SKU. These SKUs support a zone-redundant setup and are, by default, associated with Standard IPs. This setup ensures that even if one zone experiences issues, the virtual network gateway infrastructure remains operational due to the distribution across multiple zones. For a deeper understanding of zone redundant gateways, please refer to [Availability Zone deployments.](../reliability/availability-zones-overview.md)
 
 ## Gateway migration experience
+Historically, users had to use the Resize-AzVirtualNetworkGateway PowerShell command or delete and recreate the virtual network gateway to migrate between SKUs.
 
-The new guided gateway migration experience enables you to migrate from a Non-Az-Enabled SKU to an Az-Enabled SKU. With this feature, you can deploy a second virtual network gateway in the same GatewaySubnet and Azure automatically transfers the control plane and data path configuration from the old gateway to the new one.
+With the guided gateway migration experience you can deploy a second virtual network gateway in the same GatewaySubnet and Azure automatically transfers the control plane and data path configuration from the old gateway to the new one. During the migration process, there will be two virtual network gateways in operation within the same GatewaySubnet. This feature is designed to support migrations without downtime. However, users may experience brief connectivity issues or interruptions during the migration process.
+## Supported migration scenarios
+The guided gateway migration experience supports any-to-any SKU migration. However, it is recommended to migrate to an Az-enabled SKU. 
 
 ### Limitations
 
 The guided gateway migration experience doesn't support these scenarios:
-
-* ExpressRoute/VPN coexistence
-* Azure Route Server 
-* FastPath connections
+* Migration to a virtual network gateway SKU configured with a Basic IP
 
 Private endpoints (PEs) in the virtual network, connected over ExpressRoute private peering, might have connectivity problems during the migration. To understand and reduce this issue, see [Private endpoint connectivity](expressroute-about-virtual-network-gateways.md#private-endpoint-connectivity-and-planned-maintenance-events).
 
+## Common Validation Errors
+In the gateway migration experience, you will need to validate if your resource is capable of migration. Here are some Common migration errors: 
+
+### Virtual Network 
+* Gateway Subnet needs two or more prefixes for migration.
+* MaxGatewayCountInVnetReached – Reached maximum number of gateways that can be created in a Virtual Network. 
+
+### Connection 
+The virtual network gateway connection resource is not in a succeed state. 
+
 ## Enroll subscription to access the feature
 
 1. To access this feature, you need to enroll your subscription by filling out the [ExpressRoute gateway migration form](https://aka.ms/ergwmigrationform).
 
-1. After your subscription is enrolled, you'll get a confirmation e-mail with a PowerShell script for the gateway migration.
+1. After your subscription is enrolled, you'll get a confirmation e-mail with a PowerShell script or a link to the Azure Portal for the gateway migration.
 
 ## Migrate to a new gateway