Cloud ACI 5.2: ACI/Azure Tenant vNET Peering across Azure Acitive Directories

From Cloud APIC 5.2 you can configure Tenant vNET peerings across Azure Active Directories. This will be very useful for B2B connectivity. Prior to this tenant vNET peerings for Azure using cAPIC was only possible across subscriptions in the same Azure Active Directory.

To Follow along this Proof Of Concept Lab in your own Azure subscriptions, you will need the following:

Pre-Requisites:

• You will need 2 Azure Active Directories With 1 Subscription in each.
• AD1/Subscription1:  Running cApic 5.2, Infra Tenant
• AD2/Subscription1:  Will be used for User Tenant

VNET peering across Azure Active Directories

• Prior to 5.2 release, VNET peering (cAPIC managed) could not be established between two VNETs if they belonged to two different subscriptions corresponding to different Azure Active Directories.
• Azure Active Directory (Azure AD) is Microsoft’s enterprise cloud-based identity and access management (IAM) solution
• An Azure subscription has a trust relationship with Azure AD. A subscription trusts Azure AD to authenticate users, services, and devices.
• In 5.2 release, VNET peering across Active Directories is supported. Thus, the spoke VNETs can be deployed in subscriptions in different Azure ADs.

Recap: Azure Active Directory

• Azure Active Directory (Azure AD) is Microsoft’s enterprise cloud-based identity and access management (IAM) solution
• An Azure subscription has a trust relationship with Azure AD. A subscription trusts Azure AD to authenticate users, services, and devices.
• Multiple subscriptions can trust the same Azure AD directory.
• Each subscription can only trust a single directory. One or more Azure subscriptions can establish a trust relationship with an instance of Azure Active Directory (Azure AD) in order to authenticate and authorize security principals and devices against Azure services.

Considerations:

• What this feature allows:
• Allow the Infra VNETs and Spoke VNETs to be in different Azure ADs
• Spokes can be spread across multiple different subscriptions across different Azure ADs
• What this feature doesn’t allow:
• Infra VNETs in a given site cannot be deployed or split across multiple different subscriptions. All the Infra VNETs in a site need to belong to the same subscription which means same Azure AD.

Managed Identity
Existing Infra Tenant and User Tenant’s Account Config:

• Prior to 5.2 release, only ”Managed Identity” was supported for Infra Tenant’s Authorization or Credentials. For user tenants, both “Managed Identity” and “Service Principal” were supported.
• To support VNET Peering across Azure ADs, both the Infra and User Tenants must use the Account only in Service-Principal mode.  In Release 5.2 support for Service Principal is now an option for Infra Tenant. This makes VNET peering possible when Infra Subscription and Tenant Subscriptions are in different Azure ADs.
• VNET Peering across the Azure ADs can only be achieved by using Service Principal mode of Authorization on Azure. This cannot be achieved using the Managed Identity.
• This limitation comes from the Azure SDK where this can be done only using the service Principal mode of credentials.
• If Peering between VNETs across multiple Azure ADs is NOT required, then they can continue to use the existing Managed Identity for both users and Infra Tenants.

Note: Managed Identity and Service Principal
Managed Identity

• Managed identities provide an identity for applications to use when connecting to resources that support Azure Active Directory (Azure AD) authentication. Applications may use the managed identity to obtain Azure AD tokens. For example, an application may use a managed identity to access resources like Azure Key Vault where developers can store credentials in a secure manner or to access storage accounts.
• Here are some of the benefits of using Managed identities:
• You don’t need to manage credentials. Credentials are not even accessible to you.
• You can use managed identities to authenticate to any resource that supports Azure Active Directory authentication including your own applications.
• Managed identities can be used without any additional cost.
• https://docs.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/overview

In Case you are wondering why we were able to create ACI Tenants in different subscription from Infra Tenant Subscription using VNG (VPN Gateway) but for VNET Peering there are extra Service Principal configurations involved, then the below will hopefully clarify that.

• Prior to release 5.2. when we needed to build the User Tenant in a different Azure AD from the Infra Tenant Azure AD, we needed to create a Service Principal (unmanaged identity) in the Tenant Subscription. This allowed us to establish VPN Gateway connectivity between Infra VNET and Tenant VNET.  The cAPIC was given the Service Principal credentials of the Tenant Account and the cAPIC was able to configure items in the Tenant Subscription in different Azure AD.
• In 5.2, if you wanted to use VNET Peering instead of VPN Gateway between Infra Tenant Subscription and User Tenant Subscription, then each of these subscriptions would need roles to establish the VNET Peering to the other Subscription. For that reason, we would need to now create Service Principals in both Infra Tenant AD and User Tenant AD. Then a trust relationship has to be built so that the Service Principal on each AD is allowed to build the VNET Peering from its AD/subscription VNET to the other AD/subscription VNET.

What We Will Do In This Lab:

In this guided step by step example, we intend to do the following:

• ACI Infra Tenant is present in Azure AD1/Subscription1 (that’s where cAPIC resides)
• We intend to build a User Tenant in Azure AD2/Subscription1 which will be part of the cAPiC Fabric
• We also want to have VNET Peering between User Tenant and Infra Tenant instead of using VNG

What we need to do to make the above work:

1. Create Service Principal “ACI-Infra-SP” in Azure AD1 and give the role of Contributor to that Service Profile for AD1/Subscription1
2. Create Service Principal “ACI-Tenant-SP”  in Azure AD2 and give the role of Contributor to that Service Profile for AD2/Subscription1
3. Give Consent for ”ACI-Infra-SP” to be able to be used for other ADs
4. Give Consent for “ACI-Tenant-SP” to be able to be used for other ADs
7. Go to cAPIC and change Infra Tenant to use Service Principal instead of using Managed Identity
8. Build a simple ACI Tenant (use Service Principal) in AD2/Subscription1 and use VNET Peering instead of VNG
9. Verify

Go to Azure Active Directory  for Infra Tenant Subscription and click on App registrations and add New registration

As you continue on creating the Service Principal, please follow the below figure.  It is important that you configure the Redirect URL:   https://www.microsoft.com

On the overview of the SP,  look at the relevant information and jot it down to a text file

Now,  click on “Certificates & Secrets” and create either Certificate or Client Secret.  In this example, I’ll keep it simple and create Client Secret

Name the Client Secret

Add the secret information and jot  down the info in the same text file

ACI-Infra-SP Service Principal  and Client Secret has been created.

Please  now make the Service Principal  “ACI-Tenant-SP” on  AZ AD2.  I will not show it here, just repeat the same process.

Once Done, we need to give each SP (in each AD)  the roles of Contributor for its subscription.  Let’s start giving Contributor Role for the Infra Tenant Subscription.

Select Contributor Role, Assign to Service Principal, in the Select box, type in ACI.  You will get a match on ACI-Infra-SP.  Click on that and add it in.

Note that we also need to add in the Service Principal of the other AZ Directory “ACI-Tenant-SP” here as a Network Contributor.  However, it’s not showing up at this time !

We’ll deal with that a little bit later

Now, go ahead and repeat the same process for Contributor role assignment process of ACI-Tenant-SP  for AD2/Subscription1.  I will not show it here.

Now, it’s time to work on giving cross account Service Principal Roles.  For this we will need to finish off the Microsoft Consent Process.   To do this you will need to create a URI and browse to it.  The URI format is shown below.  However, let’s do this with a simple bash script to make it much easier and error free.

Copy and Paste the below on your MAC Terminal or Ubuntu Terminal Shell.  Make sure to choose everything below:

cat > getURI.sh <<EOF#!/bin/bash# Modify the Infra Dir ID   and Infra APP Id belowINFRADIR_ID="c10d8d5a-afd8-49af-ba49-5ca83470cd06"INFRAAPP_ID="5d6b7cdb-2400-48b2-9fae-1041e73e2e45"# Modify the Tenant Dir ID   and Tenant APP Id belowTENANTDIR_ID="01f0541f-adbe-45d4-b69a-309545208f6d"TENANTAPP_ID="845371a4-291d-4e7a-9d6f-1a00297c9dd4"echoechoecho  "use the below uri for ACI-Infra-SP consent"echo "https://login.microsoftonline.com/$TENANTDIR_ID/oauth2/authorize?client_id=$INFRAAPP_ID&response_type=code&redirect_uri=https%3A%2F%2Fwww.microsoft.com%2F"echoechoecho  "use the below uri for ACI-Tenant-SP consent"echo "https://login.microsoftonline.com/$INFRADIR_ID/oauth2/authorize?client_id=$TENANTAPP_ID&response_type=code&redirect_uri=https%3A%2F%2Fwww.microsoft.com%2F"EOF

Next, vi the file “getURI.sh”  and populate the information of Infra Tenant and User Tenant you collected earlier.  Example of my setup is shown in the figure below.

Now, make the shell script executable and run it to obtain the 2 URIs needed

Browse the the first URI from a browser

Repeat the steps for consent using the 2nd URI from script output.  I will not show it here.

Now go back to IAM of each subscription (from Azure UI) and add in the cross Role for the Service Principals as shown below. This was not possible until we finished the consent.

The Final Roles should show as below:

You are all done to enable building ACI Tenants using vNET Peering (across Azure Active Directories) instead of VNG

Conclusion:  We have verified that from cAIC release 5.2, Tenant vNET peerings across Azure Active Directories is now possible. This will be very useful for B2B connectivity. Prior to this tenant vNET peerings for Azure using cAPIC was only possible across subscriptions in the same Azure Active Directory.

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