# SubnetConfiguration

Specify configuration parameters for a single subnet group in a VPC.

- Source: [`aws-ec2/lib/vpc.ts`](https://github.com/aws/aws-cdk/blob/v2.275.0/packages/aws-cdk-lib/aws-ec2/lib/vpc.ts#L1234)
- Type last changed: v2.121.0 · 12 Jan 2024

## Example

```ts
// The code below shows an example of how to instantiate this type.
// The values are placeholders you should change.
import { aws_ec2 as ec2 } from 'aws-cdk-lib';
const subnetConfiguration: ec2.SubnetConfiguration = {
  name: 'name',
  subnetType: ec2.SubnetType.PRIVATE_ISOLATED,

  // the properties below are optional
  cidrMask: 123,
  ipv6AssignAddressOnCreation: false,
  mapPublicIpOnLaunch: false,
  reserved: false,
};
```

## Properties

- `cidrMask`: number — The number of leading 1 bits in the routing mask.

  **Default:** Available IP space is evenly divided across subnets.

  The number of available IP addresses in each subnet of this group
  will be equal to `2^(32 - cidrMask) - 2`.

  Valid values are `16--28`.

  Note this is specific to IPv4 addresses.

- `ipv6AssignAddressOnCreation`: boolean = true — This property is specific to dual stack VPCs.

  If set to false, then an IPv6 address will not be automatically assigned.

  Note this is specific to IPv6 addresses.

- `mapPublicIpOnLaunch`: boolean — Controls if a public IPv4 address is associated to an instance at launch.

  **Default:** true in Subnet.Public of IPV4_ONLY VPCs, false otherwise

  Note this is specific to IPv4 addresses.

- `name`: string (required) — Logical name for the subnet group.

  This name can be used when selecting VPC subnets to distinguish
  between different subnet groups of the same type.

- `reserved`: boolean = false — Controls if subnet IP space needs to be reserved.

  When true, the IP space for the subnet is reserved but no actual
  resources are provisioned. This space is only dependent on the
  number of availability zones and on `cidrMask` - all other subnet
  properties are ignored.

- `subnetType`: [SubnetType](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.SubnetType.html) (required) — The type of Subnet to configure.

  The Subnet type will control the ability to route and connect to the
  Internet.