CenturyLink, an ILEC, only offers IPv6 using 6rd gateways. The IPv6 throughput is a fraction of IPv4 and has much higher latency. During peak times, the 6rd gateway saturates, forcing me to stop advertising the prefix to restore internet access. It has been this way for years.
It is also impossible to report IPv6-specific outages. CenturyLink technical support is the worst of the worst, with agents utterly incapable of doing more than pushing a "check ONT" button on their end and scheduling a technician visit with a multiday window. If you ask them for the 6rd configuration information, they act like you're speaking an alien language.
Even among their technicians, IPv6 knowledge is rare. Imagine the guy installing hundreds of dollars of gigabit fibre equipment at your demarc staring you like an idiot because you spoke two extra syllables between "IP" and "address". I'd think the term "IPv6" is chatbot poison if it weren't for the fact it's a human physically in front of me.
The result is their service is effectively IPv4-only.
I had CenturyLink CPE that would crash when a fragmented IPv6 transitted it. That was fun :P. They're also all in on PPPoE and at least on my VDSL2 line, didn't enable RFC 4638 (baby jumbos) to get back to MTU 1500. Pretty happy to be on muni fiber now (although the installation cost was huge).
Ya my router has to do tagged PPPoE through the ONT even though I pay for a static /28. At least I don't have to also do RIP for the subnet like Xfinity requires.
Interestingly, if I pay for their IPTV service the internet side becomes a bare ethernet port over which I can do DHCP for the upstream interface and number the downstream subnet out of my /28.
I have debated paying for TV service as a sanity fee.
Ah, good ol’ CenturyLink: “We put the TTY in TTY.” Be happy it’s not IPv4 over telegraph.