Work with your default VPC and default subnets

This section describes how to work with default VPCs and default subnets.

View your default VPC and default subnets

You can view your default VPC and subnets using the Amazon VPC console or the command line.

Use the commands with the isDefault filter and set the filter value to true.

Use the commands with the vpc-id filter and set the filter value to the ID of the default VPC. In the output, the DefaultForAz field is set to true for default subnets.

Create a default VPC

If you delete your default VPC, you can create a new one. You cannot restore a previous default VPC that you deleted, and you cannot mark an existing nondefault VPC as a default VPC.

When you create a default VPC, it is created with the standard components of a default VPC, including a default subnet in each Availability Zone. You cannot specify your own components. The subnet CIDR blocks of your new default VPC may not map to the same Availability Zones as your previous default VPC. For example, if the subnet with CIDR block 172.31.0.0/20 was created in us-east-2a in your previous default VPC, it may be created in us-east-2b in your new default VPC.

If you already have a default VPC in the Region, you cannot create another one.

To create a default VPC using the command line

You can use the create-default-vpc AWS CLI command. This command does not have any input parameters.

aws ec2 create-default-vpc

The following is example output.

{
    "Vpc": {
        "VpcId": "vpc-3f139646", 
        "InstanceTenancy": "default", 
        "Tags": [], 
        "Ipv6CidrBlockAssociationSet": [], 
        "State": "pending", 
        "DhcpOptionsId": "dopt-61079b07", 
        "CidrBlock": "172.31.0.0/16", 
        "IsDefault": true
    }
}

Alternatively, you can use the New-EC2DefaultVpc Tools for Windows PowerShell command or the CreateDefaultVpc Amazon EC2 API action.

Create a default subnet

You can create a default subnet in an Availability Zone that does not have one. For example, you might want to create a default subnet if you have deleted a default subnet, or if AWS has added a new Availability Zone and did not automatically create a default subnet for that zone in your default VPC.

When you create a default subnet, it is created with a size /20 IPv4 CIDR block in the next available contiguous space in your default VPC. The following rules apply:

If there is not enough address space in your default VPC to create a size /20 CIDR block, the request fails. If you need more address space, you can add an IPv4 CIDR block to your VPC.

If you've associated an IPv6 CIDR block with your default VPC, the new default subnet does not automatically receive an IPv6 CIDR block. Instead, you can associate an IPv6 CIDR block with the default subnet after you create it. For more information, see Add or remove an IPv6 CIDR block from your subnet.

You cannot create a default subnet using the AWS Management Console.

To create a default subnet using the AWS CLI

Use the create-default-subnet AWS CLI command and specify the Availability Zone in which to create the subnet.

aws ec2 create-default-subnet --availability-zone us-east-2a

The following is example output.

{
    "Subnet": {
        "AvailabilityZone": "us-east-2a", 
        "Tags": [], 
        "AvailableIpAddressCount": 4091, 
        "DefaultForAz": true, 
        "Ipv6CidrBlockAssociationSet": [], 
        "VpcId": "vpc-1a2b3c4d", 
        "State": "available", 
        "MapPublicIpOnLaunch": true, 
        "SubnetId": "subnet-1122aabb", 
        "CidrBlock": "172.31.32.0/20", 
        "AssignIpv6AddressOnCreation": false
    }
}

For more information about setting up the AWS CLI, see the AWS Command Line Interface User Guide.

Alternatively, you can use the New-EC2DefaultSubnet Tools for Windows PowerShell command or the CreateDefaultSubnet Amazon EC2 API action.

Delete your default subnets and default VPC

You can delete a default subnet or default VPC just as you can delete any other subnet or VPC. However, if you delete your default subnets or default VPC, you must explicitly specify a subnet in one of your VPCs when you launch instances. If you do not have another VPC, you must create a VPC with a subnet in at least one Availability Zone. For more information, see Create a VPC.

If you delete your default VPC, you can create a new one. For more information, see Create a default VPC.

If you delete a default subnet, you can create a new one. For more information, see Create a default subnet. To ensure that your new default subnet behaves as expected, modify the subnet attribute to assign public IP addresses to instances that are launched in that subnet. For more information, see Modify the IP addressing attributes of your subnet. You can only have one default subnet per Availability Zone. You cannot create a default subnet in a nondefault VPC.