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Because AWS has started to charge for public IPv4 addresses, I'm looking into how many public IPv4 addresses my Application Load Balancers are using.

Right now, they are listening on IPv4 only, and it's obvious that the number of network interfaces scales with the amount of traffic going to the load balancer.

If I were to change them to dual-stack, which of the following would happen?

  1. The number of network interfaces with public IPv4 addresses is proportional to the amount of incoming IPv4 traffic. Thus, if there is more IPv6 traffic than IPv4 traffic, some of the network interfaces will not have public IPv4 addresses.

  2. Each network interface has both an IPv4 and an IPv6 address, meaning that the number of public IPv4 addresses used is proportional to the total amount of incoming traffic regardless of protocol.

I couldn't find anywhere in the documentation that states one way or the other.

Tim
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legoscia
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1 Answers1

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I would make a guess that each interface would keep an IPv4 and IPv6 address, because why would AWS cripple their managed service? I doubt if you would find any documentation on this yet.

For my personal EC2 server I've made it IPv6 only and put a free CloudFlare CDN in front of it. CloudFlare provide IPv4 and IPv6 entry points but only connects to the back end server using IPv6. According to the comments below CloudFront cannot do this yet, so that's a definite advantage for CloudFlare and possibly other CDNs, which I expect AWS will address at some point in late 2023 / 2024.

Tim
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  • CloudFront currently doesn't support it. From [this blog post](https://aws.amazon.com/blogs/aws/ipv6-support-update-cloudfront-waf-and-s3-transfer-acceleration/): "Connections to your origin servers will be made using IPv4." – legoscia Aug 01 '23 at 09:10
  • Adding to what @legoscia said, the dual stack part (serving content using IPv4 and IPv6) is supported, but connecting back is IPv4 only. Though based on the change to start charge for public IPv4 addresses in 2024 I'm hopeful that this limitation will be removed. – Tim P Aug 01 '23 at 13:47