Losing internet connection???

You're right in that switching to Link-Local Only is a workaround, but per my understanding it will not affect your connection speeds or resolution speeds. What it does is essentially disable IPv6 on the external interface of the Airport Extreme (to Cox and the outside world) while still allowing devices in your local network to use IPv6 to communicate. The DNS servers you've switched to are Google servers if I'm not mistaken, which is fine, but should not have been necessary unless for some reason Cox's legacy IPv4 DNS servers started acting up in your area.

Switching to Link-Local Only should nullify the adverse effects of Cox's rollout to IPv6. It is a workaround in the sense that it also means that your connection to the internet will support IPv4 only until this is switched back to native. However today this workaround is unlikely to cause much of an issue for the following reasons.

1) There are currently no sites or services that I'm aware of that require an IPv6 connection or that would benefit substantially from one, at least as things are now, the internet still has to maintain compatibility with IPv4 and things are likely to stay that way at least for the next few years.

2) As I understand it at one time Link-Local Only used to be the default setting on the Airports anyway when IPv6 was still largely irrelevant. Turning IPv6 off should not make much of a difference to anything until the web starts to become more dependent on it in the future.

3) There may be security concerns with having IPv6 on. As I understand it, while with IPv4 your internal addresses were not directly accessible to the outside world (both due to the way NAT works and the firewall in the router), with IPv6 that is not the case. Each device will get a real unique IP address (being able to assign unique addresses to all devices on the planet is the point of IPv6) and this IP can be directly seen from the outside world. By default the Airport will not block incoming connections to IPv6 addresses. So the level of security implemented on all of your IPv6 compatible devices will become a lot more important once it is fully enabled.

I personally didn't have a problem disabling IPv6 for now, but I will keep an eye on things and plan to re-enable it once this issue has been resolved (either on Cox's end or via a firmware update on the Airport). IPv6 is the future after all, and eventually I'm sure that eventually any internet connection that doesn't support it will start to feel quite crippled, but by my estimates we are still a few years away from that day.

I do agree with you that this is really mostly on Cox (they probably should have given people a bit more of a heads up on this), and personally I don't find being forced to use their equipment in my local network as an acceptable solution.

but I will keep an eye on things and plan to re-enable it once this issue has been resolved (either on Cox's end or via a firmware update on the Airport).

For what it is worth, the folks that I've spoken to at Apple are hesitant to say anything about any kind of special firmware update for a specific Internet provider.......when things are working just fine with Comcast and Time Warner and other providers.

In case you are interested, here are the settings for an AirPort router with Comcast. The exact same settings work perfectly with Time Warner as well.

Note that I am NOT saying that these settings will work with Cox. A friend of mine on Cox has tried them with nothing but problems.

I've been using these settings on an AirPort Extreme with Time Warner service for the past 3-4 months, and there have been zero issues.

http://mydeviceinfo.xfinity.com/download.php?file_id=35

Found this on the cox website

Are there any known incompatibilities with IPv6?

The majority of retail home routers, especially those produced within the last few years, are fully IPv6-compatible. Cox has determined that Apple AirPort Extreme routers, including Time Capsule models, can experience Internet connectivity problems when running IPv6 on firmware versions 7.7.3 and earlier. Customers can resolve the issue by disabling IPv6 from the AirPort Utility on the iOS or OS X device. For more information and steps to resolve, contact Apple Support.

That was posted on Mar 15 2016; I have been having issues since Oct 2015. All L1 and many L2 Cox support reps, didn't know anything about IPv6. I didn't find out until I was having daily internet outages for almost 3 months on my second visit from field service. Even then, it took another month to get Cox to provide me with a workaround and stop pointing the finger at Apple.

The issue is actually with the AirPort, but disabling IPv6 does help the issue. When the internet is "not working", the actual problem is the AirPort isn't responding to DNS queries. You can still ping, ssh, telnet, or otherwise access traffic through the AirPort without issue. DNS queries (UDP) to external services also work without issue.

The AirPort DHCP server only hands out it's self-IP-address to clients for DNS queries, rather than passing the ISP DNS settings on through to the clients. Because of this, the AirPort becomes a single point of failure if it's internal DNS resolver fails to respond to queries. The internal DNS resolver seems to have an issue with DNS resolution on Cox's network. If you disable IPv6 on the AirPort, it will work for a while, but that doesn't solve the issue of the DNS resolver failing to work. Changing DNS settings on the client (override DNS in Network Preferences) will also get you back up and running, though it's a manual setting that shouldn't be needed.

I think Apple should update the AirPort firmware to allow the passthrough of the ISP DNS settings to DHCP clients. There's no need for the AirPort to be in the middle of that conversation anyway, and the ISP can and does provide redundant DNS servers in the event one is down.