As you probably know, every server and device that is connected to the Internet must have a unique IP address. Way back in 1981, RFC 791 (“Internet Protocol”) defined an IP address as a 32-bit entity, with three distinct network and subnet sizes (Classes A, B, and C – essentially large, medium, and small) designed for organizations with requirements for different numbers of IP addresses. In time, this format came to be seen as wasteful and the more flexible CIDR (Classless Inter-Domain Routing) format was standardized and put in to use. The 32-bit entity (commonly known as an IPv4 address) has served the world well, but the continued growth of the Internet means that all available IPv4 addresses will ultimately be assigned and put to use.

In order to accommodate this growth and to pave the way for future developments, networks, devices, and service providers are now in the process of moving to IPv6. With 128 bits per IP address, IPv6 has plenty of address space (according to my rough calculation, 128 bits is enough to give 3.5 billion IP addresses to every one of the 100 octillion or so stars in the universe). While the huge address space is the most obvious benefit of IPv6, there are other more subtle benefits as well. These include extensibility, better support for dynamic address allocation, and additional built-in support for security.

Today I am happy to announce that objects in Amazon S3 buckets are now accessible via IPv6 addresses via new “dual-stack” endpoints. When a DNS lookup is performed on an endpoint of this type, it returns an “A” record with an IPv4 address and an “AAAA” record with an IPv6 address. In most cases the network stack in the client environment will automatically prefer the AAAA record and make a connection using the IPv6 address.

Accessing S3 Content via IPv6
In order to start accessing your content via IPv6, you need to switch to new dual-stack endpoints that look like this:

http://bit.ly/2bkgphX

or this:

http://bit.ly/2aZJIkR

If you are using the AWS Command Line Interface (CLI) or the AWS Tools for Windows PowerShell you can use the --enabledualstack flag to switch to the dual-stack endpoints.

We are currently updating the AWS SDKs to support the use_dualstack_endpoint setting and expect to push them out to production by the middle of next week. Until then, refer to the developer guide for your SDK to learn how to enable this feature.

Things to Know
Here are some things that you need to know in order to make a smooth transition to IPv6:

Bucket and IAM Policies – If you use policies to grant or restrict access via IP address, update them to include the desired IPv6 ranges before you switch to the new endpoints. If you don’t do this, clients may incorrectly gain or lose access to the AWS resources. Update any policies that exclude access from certain IPv4 addresses by adding the corresponding IPv6 addresses.

IPv6 Connectivity – Because the network stack will prefer an IPv6 address to an IPv4 address, an unusual situation can arise under certain circumstances. The client system can be configured for IPv6 but connected to a network that is not configured to route IPv6 packets to the Internet. Be sure to test for end-to-end connectivity before you switch to the dual-stack endpoints.

Log Entries – Log entries will include the IPv4 or IPv6 address, as appropriate. If you analyze your log files using internal or third-party applications, you should ensure that they are able to recognize and process entries that include an IPv6 address.

S3 Feature Support – IPv6 support is available for all S3 features with the exception of Website Hosting, S3 Transfer Acceleration, and access via BitTorrent.

Region Support – IPv6 support is available in all commercial AWS Regions and in AWS GovCloud (US). It is not available in the China (Beijing) Region.

— Jeff;