🐛Default to EdgeIpVersion of "auto"

[ct-martin]

Describe the bug By default, tunnels can't be created on IPv6-only systems since EdgeIpVersion defaults to 4 instead of auto. This has been discussed in #842 #954 #1019 but those issues have been closed without a change in the default. While it's possible to override the systemd file, that file needs to exist first so using cloudflared service install as given in the Cloudflare Dashboard does not result in a working tunnel

To Reproduce Steps to reproduce the behavior:

1. Configure a remote tunnel in the Cloudflare Zero Trust Dashboard
2. Run the cloudflare service install ... command given by the dashboard on an IPv6-only device
3. See the command stall
4. Run systemctl status cloudflared and see that it's trying to use IPv4 even when there are no IPv4 addresses assigned to any interface (other than the 127.0.0.1 on lo)

If it's an issue with Cloudflare Tunnel:

• Tunnel ID : (did not get to registering/creating/connecting)
• cloudflared config: N/A (remote-managed tunnel)

Expected behavior IPv6 should work out of the box (with no systemd overrides needed)

Environment and versions

• OS: Debian 13 (Trixie)
• Architecture: x64
• Version: 2025.8.0

Logs and errors N/A

Additional context

• IPv6 support is something Cloudflare actively advertises, such as in this blog post (which, while it doesn't use tunnels in the example, still advertises being IPv6 ready): https://blog.cloudflare.com/amazon-2bn-ipv4-tax-how-avoid-paying/
• Not having IPv6 support by default is not well-documented unless you're looking for it, which means that, in addition to the commands in the Dashboard not being correct/complete, it requires spending time searching the docs and GitHub issues to figure out why it's happening
• Needing to override the systemd unit file adds a non-trivial amount of friction to using IPv6 and is not beginner-friendly

[eshentials]

Can I work on this?