Merge pull request #112912 from christiankuhtz/patch-310

clarification on prefix

Author: PRMerger12

articles/virtual-network/nat-gateway-resource.md

@@ -13,13 +13,13 @@ ms.devlang: na
 ms.topic: overview
 ms.tgt_pltfrm: na
 ms.workload: infrastructure-services
-ms.date: 04/24/2020
+ms.date: 04/27/2020
 ms.author: allensu
 ---
 
 # Designing virtual networks with NAT gateway resources
 
-NAT gateway resources are part of [Virtual Network NAT](nat-overview.md) and provide outbound Internet connectivity for one or more subnets of a virtual network. The subnet of the virtual network states which NAT gateway will be used. NAT provides source network address translation (SNAT) for a subnet.  NAT gateway resources specify which static IP addresses virtual machines use when creating outbound flows. Static IP addresses come from public IP address resources, public IP prefix resources, or both. A NAT gateway resource can use up to 16 static IP addresses from either.
+NAT gateway resources are part of [Virtual Network NAT](nat-overview.md) and provide outbound Internet connectivity for one or more subnets of a virtual network. The subnet of the virtual network states which NAT gateway will be used. NAT provides source network address translation (SNAT) for a subnet.  NAT gateway resources specify which static IP addresses virtual machines use when creating outbound flows. Static IP addresses come from public IP address resources, public IP prefix resources, or both. If a public IP prefix resource is used, all IP addresses of the entire public IP prefix resource are consumed by a NAT gateway resource. A NAT gateway resource can use a total of up to 16 static IP addresses from either.
 
 
 <p align="center">
@@ -56,7 +56,8 @@ The following diagram shows the writeable references between the different Azure
 
 NAT is recommended for most workloads unless you have a specific dependency on [pool-based Load Balancer outbound connectivity](../load-balancer/load-balancer-outbound-connections.md).  
 
-You can migrate from standard load balancer scenarios, including [outbound rules](../load-balancer/load-balancer-outbound-rules-overview.md), to NAT gateway. To migrate, move the public ip and public ip prefix resources from load balancer frontends to NAT gateway. New IP addresses for NAT gateway aren't required. Standard public IP and prefix can be reused as long as the total doesn't exceed 16 IP addresses. Plan for migration with service interruption in mind during the transition.  You can minimize the interruption by automating the process. Test the migration in a staging environment first.  During the transition, inbound originated flows aren't affected.
+You can migrate from standard load balancer scenarios, including [outbound rules](../load-balancer/load-balancer-outbound-rules-overview.md), to NAT gateway. To migrate, move the public ip and public ip prefix resources from load balancer frontends to NAT gateway. New IP addresses for NAT gateway aren't required. Standard public IP address resources and public IP prefix resource can be reused as long as the total doesn't exceed 16 IP addresses. Plan for migration with service interruption in mind during the transition.  You can minimize the interruption by automating the process. Test the migration in a staging environment first.  During the transition, inbound originated flows aren't affected.
+
 
 The following example is a snippet from an Azure Resource Manager template.  This template deploys several resources, including a NAT gateway.  The template has the following parameters in this example:
 
@@ -281,7 +282,10 @@ Once a SNAT port releases, it's available for use by any virtual machine on subn
 
 ### Scaling
 
-Scaling NAT is primarily a function of managing the shared, available SNAT port inventory. NAT needs sufficient SNAT port inventory for expected peak outbound flows for all subnets attached to a NAT gateway resource.  You can use public IP address resources, public IP prefix resources, or both to create SNAT port inventory.
+Scaling NAT is primarily a function of managing the shared, available SNAT port inventory. NAT needs sufficient SNAT port inventory for expected peak outbound flows for all subnets attached to a NAT gateway resource.  You can use public IP address resources, public IP prefix resources, or both to create SNAT port inventory.  
+
+>[!NOTE]
+>If you are assigning a public IP prefix resource, the entire public IP prefix will be used.  You can't assign a public IP prefix resource and then break out individual IP addresses to assign to other resources.  If you want to assign individual IP addresses from a public IP prefix to multiple resources, you need to create individual public IP addresses from the public IP prefix resource and assign them as needed instead of the public IP prefix resource itself.
 
 SNAT maps private addresses to one or more public IP addresses, rewriting source address and source port in the processes. A NAT gateway resource will use 64,000 ports (SNAT ports) per configured public IP address for this translation. NAT gateway resources can scale up to 16 IP addresses and 1M SNAT ports. If a public IP prefix resource is provided, each IP address within the prefix is providing SNAT port inventory. And adding more public IP addresses increases the available inventory SNAT ports. TCP and UDP are separate SNAT port inventories and unrelated.