I'm not sure where to report this in terms of AT&T, but we have over 60 AT&T sites across the Southeast area that are all having issues accessing many different parts of the Internet. These sites range from AT&T Fiber Business (GPON-based), AT&T Fiber Commercial (fiber, non-GPON-based), and AT&T Fiber Residential.
All of them, at 2:45 AM on Saturday, started having issues accessing certain parts of the Internet. I can only speak about IPv4, and can only 100% confirm that we can't ping or connect to Cox IPs, some YouTube IPs, some AWS IPs, and a few other datacenters' IPs. These sites I'm referring to are spread out physically. They all have a few private VPNs to IPv4 IPs that we use for management, and all of them dropped at 2:40 AM. All we can see are a few UDP packets since then attempting to reconnect but failing. We can connect directly to these sites from other AT&T sites, but pings or TCP connections from those sites to several other external sites fail. (Although they are not totally down, you can still access large parts of the Internet.)
It's unbelievable that this is still going on nearly 12 hours after.
I'm posting this here to confirm to others and hopefully someone at AT&T will see this. THIS is NOT a DNS issue / not your DNS server setting issue — however, those who report changing their DNS server fixes it, it may just be because doing that change refreshes your DNS cache and you happen to get a new IP address to XYZ service that also happens to be accessible (but the prior IPs via AT&T are still not accessible).
Source: r/ATTFiber · by /u/jimmy58743