# Compare IPv4 and IPv6
<a name="ipv4-ipv6-comparison"></a>

The following table summarizes the differences between IPv4 and IPv6 in Amazon EC2 and Amazon VPC.

For a list of AWS services that support dual-stack configuration (IPv4 and IPv6) and IPv6-only configurations, see [Services that support IPv6](aws-ipv6-support.md#ipv6-service-support).


| Characteristic | IPv4 | IPv6 | 
| --- | --- | --- | 
| VPC size | Up to 5 CIDRs from /16 to /28. This [quota](amazon-vpc-limits.md#vpc-limits-vpcs-subnets) is adjustable. | Up to 5 CIDRs from /44 to /60 in increments of /4. This [quota](amazon-vpc-limits.md#vpc-limits-vpcs-subnets) is adjustable. | 
| Subnet size | From /16 to /28. | From /44 to /64 in increments of /4. | 
| Address selection | You can choose the IPv4 CIDR block for your VPC or you can allocate a CIDR block from Amazon VPC IP Address Manager (IPAM). For more information, see [What is IPAM?](https://docs.aws.amazon.com/vpc/latest/ipam/what-it-is-ipam.html) in the Amazon VPC IPAM User Guide.  | You can bring your own IPv6 CIDR block to AWS for your VPC, choose an Amazon-provided IPv6 CIDR block, or you can allocate a CIDR block from Amazon VPC IP Address Manager (IPAM). For more information, see [What is IPAM?](https://docs.aws.amazon.com/vpc/latest/ipam/what-it-is-ipam.html) in the Amazon VPC IPAM User Guide.  | 
| Internet access | Requires an [internet gateway](VPC_Internet_Gateway.md). | Requires an internet gateway. Supports outbound-only communication using an [egress-only internet gateway](egress-only-internet-gateway.md). | 
| Elastic IP addresses | Supported. Gives an EC2 instance a permanent, static public IPv4 address. | Not supported. EIPs keep the public IPv4 address of an instance static on instance restart. IPv6 addresses are static by default. | 
| NAT gateways |  Supported. Instances in private subnets can connect to the internet using a public NAT gateway or to resources in other VPCs using a private NAT gateway.  | Supported. You can use a NAT gateway with NAT64 to enable instances in IPv6-only subnets to communicate with IPv4-only resources within VPCs, between VPCs, in your on-premises networks, or over the internet. | 
| DNS names | Instances receive Amazon-provided IPBN or RBN-based DNS names. The DNS name resolves to the DNS records selected for the instance. | Instance receive Amazon-provided IPBN or RBN-based DNS names. The DNS name resolves to the DNS records selected for the instance. |