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Configure custom BGP communities for Azure ExpressRoute private peering

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BGP communities are groupings of IP prefixes tagged with a community value. This value can be used to make routing decisions on the router's infrastructure. You can apply filters or specify routing preferences for traffic sent to your on-premises from Azure with BGP community tags. This article explains how to apply a custom BGP community value for your virtual networks using Azure PowerShell. Once configured, you can view the regional BGP community value and the custom community value of your virtual network. This value will be used for outbound traffic sent over ExpressRoute when originating from that virtual network.

Prerequisites

  • Review the prerequisites, routing requirements, and workflows before you begin configuration.

  • You must have an active ExpressRoute circuit.

    • Follow the instructions to create an ExpressRoute circuit and have the circuit enabled by your connectivity provider.
    • Ensure that you have Azure private peering configured for your circuit. See the configure routing article for routing instructions.
    • Ensure that Azure private peering gets configured and establishes BGP peering between your network and Microsoft for end-to-end connectivity.

Working with Azure PowerShell

The steps and examples in this article use Azure PowerShell Az modules. To install the Az modules locally on your computer, see Install Azure PowerShell. To learn more about the new Az module, see Introducing the new Azure PowerShell Az module. PowerShell cmdlets are updated frequently. If you are not running the latest version, the values specified in the instructions may fail. To find the installed versions of PowerShell on your system, use the Get-Module -ListAvailable Az cmdlet.

You can use Azure Cloud Shell to run most PowerShell cmdlets and CLI commands, instead of installing Azure PowerShell or CLI locally. Azure Cloud Shell is a free interactive shell that has common Azure tools preinstalled and is configured to use with your account. To run any code contained in this article on Azure Cloud Shell, open a Cloud Shell session, use the Copy button on a code block to copy the code, and paste it into the Cloud Shell session with Ctrl+Shift+V on Windows and Linux, or Cmd+Shift+V on macOS. Pasted text is not automatically executed, press Enter to run code.

There are a few ways to launch the Cloud Shell:

Option Link
Click Try It in the upper right corner of a code block. Cloud Shell in this article
Open Cloud Shell in your browser. https://shell.azure.com/powershell
Click the Cloud Shell button on the menu in the upper right of the Azure portal. Cloud Shell in the portal

Apply a custom BGP community value for a new virtual network

  1. To start the configuration, sign in to your Azure account and select the subscription that you want to use.

    If you are using the Azure Cloud Shell, you sign in to your Azure account automatically after clicking 'Try it'. To sign in locally, open your PowerShell console with elevated privileges and run the cmdlet to connect.

    Connect-AzAccount

    If you have more than one subscription, get a list of your Azure subscriptions.

    Get-AzSubscription

    Specify the subscription that you want to use.

    Select-AzSubscription -SubscriptionName "Name of subscription"

  2. Create a resource group to store the new virtual network.

    $rg = @{
    Name = 'myERRG'
    Location = 'WestUS'
}
New-AzResourceGroup @rg

  3. Create a new virtual network with the -BgpCommunity flag to apply a BGP community value.

    $vnet = @{
    Name = 'myVirtualNetwork'
    ResourceGroupName = 'myERRG'
    Location = 'WestUS'
    AddressPrefix = '10.0.0.0/16'
    BgpCommunity = '12076:20001'    
}
New-AzVirtualNetwork @vnet

    Note

    The 12076: is required before your custom community value.

  4. Retrieve your virtual network and review its properties. You'll notice a BgpCommunities section that contains a RegionalCommunity value and a VirtualNetworkCommunity value. The RegionalCommunity value is predefined based on the Azure region of the virtual network. The VirtualNetworkCommunity value should match your custom definition.

    $virtualnetwork = @{
    Name = 'myVirtualNetwork'
    ResourceGroupName = 'myERRG'
} 
Get-AzVirtualNetwork @virtualnetwork

Applying or updating the custom BGP value for an existing virtual network

  1. Get the virtual network you want to apply or update the BGP community value and store it to a variable.

    $virtualnetwork = @{
    Name = 'myVirtualNetwork'
    ResourceGroupName = 'myERRG'
} 
$vnet = Get-AzVirtualNetwork @virtualnetwork

  2. Update the VirtualNetworkCommunity value for your virtual network.

    $vnet.BgpCommunities = @{VirtualNetworkCommunity = '12076:20002'}
$vnet | Set-AzVirtualNetwork

    Note

    The 12076: is required before your custom community value.

  3. Retrieve your virtual network and review its updated properties. The RegionalCommunity value is predefined based on the Azure region of the virtual network; to view the regional BGP community values for private peering, see ExpressRoute routing requirements. The VirtualNetworkCommunity value should match your custom definition.

    $virtualnetwork = @{
    Name = 'myVirtualNetwork'
    ResourceGroupName = 'myERRG'
} 
Get-AzVirtualNetwork @virtualnetwork

Next steps