I was having a debate with someone on this. Take a critical web site,
say one where you want 100% global uptime, no potential issues with end
users having connectivity or routing issues getting to your IP. Would it
be advantageous to purposely not support a AAAA record in DNS and
disable IPv6, only exist on IPv4?
No
My argument against this was "Broken IPv6 Connectivity" doesn't really
occur anymore, also, almost all browsers and OS IP stacks implement
Happy Eyeballs algorithm where both v4 and v6 are attempted, so if v6
dies it will try v4. I would also argue that lack of IPv6 technically
makes the site unreachable from native IPv6 clients, and in the event of
an IPv4 outage, connectivity might still remain on IPv6 if the site had
an IPv6 address (I've experienced scenarios with a bad IPv4 BGP session,
but the IPv6 session remained up and transiting traffic...)
Thoughts?
Correct, the broken ipv6 thing is super rare and those rare event are solved with Happy eyeballs.
There are well over 100 million ipv6-only Android and iOS devices in north america alone. Failing to deploy ipv6 on the website means they get to share capacity on a CGN, ip repution issues, and indirection to reach the CGN.
FB, Google, Netflix, Akamai and other push ipv6 because it is good for business, the business of running money making content.
-John