Update application-gateway-dns-resolution.md

Author: jaesoni

articles/application-gateway/application-gateway-dns-resolution.md

@@ -24,7 +24,7 @@ Application Gateway performs DNS resolution for the Fully Qualified Domain Names
 2) **Management FQDNs** that are utilized for various Azure infrastructure endpoints (control plane). These are the building blocks that form a complete Application Gateway resource. For example, communication with monitoring endpoints enable flow of Logs and Metrics. Thus, it is important for application gateways to internally communicate with other Azure services' endpoints having suffixes like `.windows.net`, `.azure.net`, etc.
 
 > [!IMPORTANT]
-> The management endpoint domain names that an Application Gateway resource interacts with are listed here. Depending on the type of application gateway deployment (detailed in this article), any name resolution issue for FQDNs with domain names may lead to either partial or complete loss of resource functionality.
+> The management endpoint domain names that an Application Gateway resource interacts with are listed here. Depending on the type of application gateway deployment (detailed in this article), any name resolution issue for these Azure domain names may lead to either partial or complete loss of resource functionality.
 > 
 > * .windows.net
 > * .chinacloudapi.cn
@@ -47,23 +47,24 @@ The Azure-provided DNS comes as a default setting with all virtual networks in A
 
 :::image source="media/application-gateway-dns-resolution/default-dns.png" alt-text="A diagram showing DNS resolution for Azure-provided DNS.":::
 
-**Flow**
-
-In this diagram, we can see,
-* The Application Gateway instance talks to Azure-provided DNS (168.63.129.16) for name resolution of the backend servers FQDN "server1.contoso.com" and "server2.contoso.com", as shown with blue line.
+Flows: 
+* In this diagram, we can see the Application Gateway instance talks to Azure-provided DNS (168.63.129.16) for name resolution of the backend servers FQDN "server1.contoso.com" and "server2.contoso.com", as shown with blue line.
 * Similarly, the instance reaches out 168.63.129.16 for the name resolution of private link-enabled Key Vault resource, as shown in orange line. To allow an application gateway to DNS resolve the key vault endpoint to its private IP, it is important to link the Private DNS zone to that application gateway’s virtual network.
 * After performing successful DNS resolutions for these FQDNs, the instance can communicate with the Key Vault and backend server endpoints.
 
-**Considerations** 
-
+Considerations:
 * Do not create and link private DNS zones for top-level Azure domain names. You must create DNS zone for a subdomain as specific as possible. For example, having a private DNS zone for `privatelink.vaultcore.azure.net` for a key vault’s private endpoint works in all cases than having a zone for `vaultcore.azure.net` or `azure.net`.
 * For communication with backend servers or any service using a Private Endpoint, ensure the private link DNS zone is linked to your application gateway’s virtual network. 
 
+#### Using custom DNS servers
 
+In your virtual network, it is possible to designate custom DNS servers. This configuration may be required for managing zones independently for specific domain names. Such an arrangement directs the application gateway instances within the virtual network also to utilize the specified custom DNS servers for resolving non-Azure domain names. 
 
+:::image source="media/application-gateway-dns-resolution/custom-dns.png" alt-text="A diagram showing DNS resolution with custom DNS servers.":::
 
-
-
+Flows: 
+* The diagram shows that the Application Gateway instance uses Azure-provided DNS (168.63.129.16) for name resolution of the private link Key Vault endpoint "contoso.privatelink.vaultcore.azure.net". The DNS queries for Azure domain names, which includes `azure.net`, are redirected to Azure-provided DNS. Shown in orange line.
+* For DNS resolution of "server1.contoso.com", the instance honors the custom DNS setup, as shown in blue line.