Cloudflare IPV6 behaviour
How does Cloudflare behave in situations where a user supports both Ipv4 and Ipv6? I've read https://developers.cloudflare.com/network/ipv6-compatibility/ but the wording makes me a bit unsure about if it is referring about doing Ipv6 to the upstream servers or if it will prefer to use Ipv4 if a client has dualstack support.
Cloudflare Docs
IPv6 compatibility | Cloudflare Network settings docs
Cloudflare enables IPv6 on all domains without requiring additional configuration or hardware (as long as your host provides IPv6 support).
6 Replies
Unfortunately my own ISP doesn't do Ipv6 currently, so it is a bit of a PITA to test locally
That is user -> Cloudflare
Okay, so I should expect if a user supports both, we'll get the ipv4 address in the connecting IP header since cloud flare prefers ipv4?
Correct
👍 thanks
Cloudflare prefers IPv4 over IPv6 for origin connections. If, in Cloudflare, you have a proxied A and proxied AAAA for the same name, CF will use A/IPv4 to connect to your origin.
Clients use Happy Eyeballs and prefer IPv6. If the user supports both, you will generally see IPv6 being used and thus CF-Connecting-IP being their IPv6, but that is client/browser behavior so it can depend and isn't a CF thing. Both Firefox and Chrome use Happy Eyeballs and prefer IPv6 though