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Managing prefix allocations for Amazon Direct Connect virtual interfaces - Amazon Direct Connect
PrerequisitesView prefix poolSet allocation on new VIFUpdate allocation on existing VIFView gateway allocationsVerify the allocation changeTroubleshooting
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Managing prefix allocations for Amazon Direct Connect virtual interfaces

You can manage the number of inbound route prefixes allocated to each virtual interface on your Direct Connect connection. Use the Amazon Management Console, Amazon CLI, or Amazon SDKs to view your connection's prefix pool, allocate prefixes to virtual interfaces, and adjust allocations as your routing needs change.

Important

If the number of advertised prefixes on a virtual interface exceeds the allocated count, the BGP session on that virtual interface goes to an idle state (BGP DOWN). Ensure that your allocation is at least as large as the number of prefixes you plan to advertise.

Prerequisites

Before you manage prefix allocations, ensure that you have the following:

  • An active Direct Connect dedicated connection or LAG.

  • At least one private or transit virtual interface.

  • Permissions to call Direct Connect APIs (directconnect:DescribeConnections, directconnect:DescribeVirtualInterfaces, directconnect:DescribeDirectConnectGateways, directconnect:UpdateVirtualInterfaceAttributes, directconnect:CreatePrivateVirtualInterface, directconnect:CreateTransitVirtualInterface).

View your connection's prefix pool

You can view the prefix pool for your connection to determine how many prefixes are available and how they are allocated across your virtual interfaces.

Console
To view your connection's prefix pool

  1. Open the Amazon Direct Connect console at https://console.amazonaws.cn/directconnect/v2/home.

  2. In the navigation pane, choose Connections.

  3. Select your connection.

  4. On the connection details page, locate the Inbound prefixes card.

  5. Review the following values: Pool size, Unallocated, and Allocated. IPv4 and IPv6 values are shown separately.

Command line

Use the describe-connections command.

aws directconnect describe-connections \
    --connection-id dxcon-abc12345

In the response, check the following fields:

  • prefixPoolSizeIpv4 and prefixPoolSizeIpv6 — The total number of prefixes in the pool.

  • prefixPoolUnallocatedCountIpv4 and prefixPoolUnallocatedCountIpv6 — The number of prefixes that are not allocated to a virtual interface.

Set the prefix allocation when creating a virtual interface

You can set the prefix allocation for a virtual interface when you create it. This reserves a portion of the connection's prefix pool for the new virtual interface.

Console
To set the prefix allocation when creating a virtual interface

  1. Open the Amazon Direct Connect console at https://console.amazonaws.cn/directconnect/v2/home.

  2. In the navigation pane, choose Virtual Interfaces.

  3. Choose Create virtual interface.

  4. Configure the virtual interface settings, including the type, VLAN, and BGP ASN.

  5. In the Inbound prefix allocation section, enter the number of IPv4 and IPv6 prefixes to allocate.

  6. Choose Create virtual interface.

Command line

Use the create-private-virtual-interface command. The following example creates a private virtual interface with prefix allocations.

aws directconnect create-private-virtual-interface \
    --connection-id dxcon-abc12345 \
    --new-private-virtual-interface '{
        "virtualInterfaceName": "my-private-vif",
        "vlan": 101,
        "asn": 65000,
        "directConnectGatewayId": "d2113d06-a0d8-476b-91a7-8555d9973d12",
        "prefixPoolAllocatedCountIpv4": 500,
        "prefixPoolAllocatedCountIpv6": 100
    }'

Update the prefix allocation on an existing virtual interface

You can update the prefix allocation on an existing virtual interface to increase or decrease the number of prefixes reserved for that interface.

Console
To update the prefix allocation on a virtual interface

  1. Open the Amazon Direct Connect console at https://console.amazonaws.cn/directconnect/v2/home.

  2. In the navigation pane, choose Virtual Interfaces.

  3. Select the virtual interface that you want to update.

  4. Choose Edit.

  5. Update the IPv4 prefix allocation value, the IPv6 prefix allocation value, or both.

  6. Choose Update virtual interface.

Command line

Use the update-virtual-interface-attributes command.

aws directconnect update-virtual-interface-attributes \
    --virtual-interface-id dxvif-abc12345 \
    --prefix-pool-allocated-count-ipv4 500 \
    --prefix-pool-allocated-count-ipv6 100

View the Direct Connect gateway total prefix allocations

You can view the total prefix allocations across all virtual interfaces attached to a Direct Connect gateway.

Console
To view the Direct Connect gateway total prefix allocations

  1. Open the Amazon Direct Connect console at https://console.amazonaws.cn/directconnect/v2/home.

  2. In the navigation pane, choose Direct Connect Gateways.

  3. Select your gateway.

  4. On the gateway details page, review the Total prefix pool allocations value.

Command line

Use the describe-direct-connect-gateways command.

aws directconnect describe-direct-connect-gateways \
    --direct-connect-gateway-id d2113d06-a0d8-476b-91a7-8555d9973d12

In the response, check the totalPrefixPoolAllocations field.

Verify the allocation change

After you update a prefix allocation, the new value takes effect immediately. The BGP session remains up as long as the number of advertised prefixes does not exceed the new allocation. The API rejects requests to reduce an allocation below the number of prefixes currently in use on the VIF.

Troubleshooting

The following are common issues that you might encounter when managing prefix allocations.

BGP session goes down after adding prefixes

The number of advertised prefixes exceeded the allocated count. Increase the allocation by using the UpdateVirtualInterfaceAttributes API or the console.

Cannot decrease allocation

You cannot reduce a VIF's allocated value below the number of prefixes currently in use. First reduce the number of prefixes advertised by your on-premises device, then reduce the allocation.

Cannot increase allocation

The connection's prefix pool might be fully allocated. Check the prefixPoolUnallocatedCountIpv4 and prefixPoolUnallocatedCountIpv6 values on the connection. You might need to reduce allocations on other virtual interfaces first.

Direct Connect gateway total exceeds 10,000

The sum of all combined IPv4 and IPv6 allocations across virtual interfaces attached to a single Direct Connect gateway cannot exceed 10,000. Reduce allocations on other virtual interfaces or use a second gateway.