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Networking-DNS

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In this repository, You will find steps that will walk you through the process of setting up a hybrid environment (with Azure Public Cloud) and explore and experiment the different DNS Scenarios.

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# Azure Networking - DNS Scenarios
This repository hosts the templates and scripts that deploy Azure Cloud Services for a variety of Azure DNS scenarios. The deployments would be done in multiple steps to be able to create and simulate multiple independent scenarios while keeping the base infrastructure components reusable. 
![AzureVPNConcepts - Page 7](https://user-images.githubusercontent.com/13979783/124377335-15f75500-dcc9-11eb-9500-ca9ec0559697.png)

The following table lists the scenarios that we will be targeting

## Name Resolution Scenarios - Hybrid Network & Private DNS Zones

| Scenario  | Solution | DNS Suffix |
| ------------- | ------------- |-------------|
| Name resolution between VMs located in the same virtual network, or Azure Cloud Services role instances in the same cloud service.  | Azure DNS private zones or Azure-provided name resolution  | Hostname or FQDN
| Name resolution between VMs in different virtual networks or role instances in different cloud services.  | Azure DNS private zones or, Customer-managed DNS servers forwarding queries between virtual networks for resolution by Azure (DNS proxy). See Name resolution using your own DNS server.  |FQDN only|
| Name resolution from an Azure App Service (Web App, Function, or Bot) using virtual network integration to role instances or VMs in the same virtual network.|Customer-managed DNS servers forwarding queries between virtual networks for resolution by Azure (DNS proxy). See Name resolution using your own DNS server.|FQDN only|
|Name resolution from App Service Web Apps to VMs in the same virtual network.|Customer-managed DNS servers forwarding queries between virtual networks for resolution by Azure (DNS proxy). See Name resolution using your own DNS server.|FQDN only|
|Name resolution from App Service Web Apps in one virtual network to VMs in a different virtual network.|Customer-managed DNS servers forwarding queries between virtual networks for resolution by Azure (DNS proxy). See Name resolution using your own DNS server.|FQDN only|
|Resolution of on-premises computer and service names from VMs or role instances in Azure.|Customer-managed DNS servers (on-premises domain controller, local read-only domain controller, or a DNS secondary synced using zone transfers, for example). See Name resolution using your own DNS server.|FQDN only|
|Resolution of Azure hostnames from on-premises computers.|Forward queries to a customer-managed DNS proxy server in the corresponding virtual network, the proxy server forwards queries to Azure for resolution. See Name resolution using your own DNS server.	|FQDN only|

### Name Resolution Scenarios - Architecture Choices
| Scenario  | Solution | DNS Suffix |
| ------------- | ------------- |-------------|
| All Scenarios involving Custom DNS Servers | Multiple DNS Servers load balanced by Std ILB  | FQDN
| All Scenarios with Azure Provided DNS | Azure Firewall DNS Proxy  | FQDN
| All Scenarios with Azure Provided DNS & Custom DNS Servers | Azure Firewall DNS Proxy with Custom DNS Servers | FQDN

## Network Architecture Diagram
![AzureVPNConcepts - DNS Scenarios-NetworkArchitecture](https://user-images.githubusercontent.com/13979783/120890838-d6ced900-c622-11eb-9db7-a4954c95c569.png)

## Name Resolution- Flow Diagram
![AzureVPNConcepts - DNS Scenarios-NameResolveFlows](https://user-images.githubusercontent.com/13979783/120890848-e6e6b880-c622-11eb-8c39-936e5796ffce.png)

### Flows Explained
- 1.1 to 1.3 - Name resolution of private DNS Zone names of VMs within a private network 
  - Uses the Custom DNS Server of the Virtual Network
  - e.g name resolution of vm-dns-dev01.az-hubinternal.net from vm-dns-dev02.az-hubinternal.net
- 2.1 to 2.4 - Name resolution of private DNS Zone names of VMs in a peered Virtual Network
  - Uses the Custom DNS Server of source VNET and the peered VNET
  - e.g. name resolution of vm-dns-dev01.az-spoke1-internal.net from vm-dns-dns-dev02.az-hubinternal.net
- 3.1 to 3.3 - Name resolution of a FQDN of a VM hosted in a VNET that an App-Service or a Function-App is integrated with (regional integration)
  - Uses the Custom DNS Server of the VNET that the function app is integrated with
  - e.g name resolution of vm-dns-dev02.az-hubinternal.net from a powershell script running in the Function App
  - Note: The name resolution of vm-dns-dev02.az-spoke1-internal.net should also work from the app
- 4.1 to 4.4 - Name resolution of a FQDN of VMs hosted in the Hub Vnet and the directly peered Spoke VNet 
  - Uses the Custom DNS Server in the Hub VNet
  - e.g name resolution of vm-dns-dev02.az-hubinternal.net from an On-prem VM with the FQDN of vm-dc-primary.azhybrid.internal & the other way around
  - Note: This should work both the ways if the resolution of Network Resources in the On-Prem network from Azure is also needed. This can be made possible by configuring the On-Prem Domain based conditional forwarding in the Hub Vnet's Custom DNS Server

## References
1. [Name Resolutions for VMs & Cloud Services](https://docs.microsoft.com/en-us/azure/virtual-network/virtual-networks-name-resolution-for-vms-and-role-instances)
2. [Private DNS Scenarios](https://docs.microsoft.com/en-us/azure/dns/private-dns-scenarios)
3. [App Service Regional & Global VNET Integration](https://docs.microsoft.com/en-us/azure/app-service/web-sites-integrate-with-vnet#how-regional-vnet-integration-works)
4. [Azure PrivateEndPoint DNS Configuration Scenarios](https://docs.microsoft.com/en-us/azure/private-link/private-endpoint-dns#dns-configuration-scenarios)
5. [Azure Firewall DNS Proxy](https://azure.microsoft.com/en-us/blog/new-enhanced-dns-features-in-azure-firewall-now-generally-available/)

## Known Issues
1. The Custom Script Extention in the VM deployment to configure a forwarder with 168.63.129.16 for the private DNS Zone fails. This has to be done manually after the VM deployment is completed.

## Important Note
1. The ARM Templates and Scripts should not be used in production directly. Modify and improve as seen necessary!
2. Architectue Diagrams for Steps 5 and 6 are added to the readme files inside the respective folders

Networking-DNS

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