- GitHub does not support IPv6.
- Docker containers do not have IPv6 by default.
- Many programs default to listening on 0.0.0.0 or 127.0.0.1 when they start, which means they only listen on IPv4. On Linux, listening on :: defaults to listening on both IPv4 and IPv6 simultaneously, but few programs do this. Python asyncio even disabled this feature[1].
- I've always heard that using IPv6 can sometimes lead to high latency or low bandwidth on certain websites, or even resource loading failures. Why isn’t there a convenient tool to compare these differences? It would be great if browsers could switch between IPv4-only, IPv6-only, and dual-stack modes. I’d like to seriously compare the effects on some websites rather than being silently affected.
- Two large ISPs, Hurricane Electric and Cogent, do not have IPv6 peering[2], so they are not interconnected, and many other ISPs have similar issues.
- Very few VPS providers offer /64 IPv6 addresses, which would allow different containers to be assigned freely within a machine. Some only provide a single /128, while others offer very few addresses per machine.
- Many people might only know how to use iptables/nftables for firewalls and forget about IPv6, leading to situations where using IPv6 can bypass the firewall. I’m not talking about issues caused by the lack of NAT (NAT is not a good firewall!), but more generally about cases where you want to disable forwarding between two network interfaces.
I stumbled upon two old posts that I found quite amusing:
In 2011, someone said[3] “It's not terribly useful to have IPv6 only websites at the moment. Check back in 5-10 years though ;)”
In 2014, someone said[4] “The Internet is growing really fast, in a few years, the IPv6 network will be bigger than IPv4, so, with IPv4, you'll be out of the real Internet. Go ahead man! Upgrade your IP!! Change is a good thing.”
[1]: https://github.com/python/cpython/blob/5f5c0b9c23238dc0a1fdb...
[2]: https://adminhacks.com/broken-IPv6.html
[3]: https://www.reddit.com/r/ipv6/comments/gnh69/what_ipv6only_w...
[4]: https://askubuntu.com/questions/309461/how-to-disable-ipv6-p...