We recently had a client install a new AT&T Fiber line for Internet access. After the line was installed, it didn't work properly. AT&T did some troubleshooting and said the line was OK. I performed some troubleshooting and noticed that one of the DNS servers 12.127.17.71 that AT&T provided was randomly timing out during a simple ping test.
I changed the DNS fowarders on the client's DNS servers to 12.127.16.67 (AT&T), 198.6.1.5 (uu.net) and 198.6.1.6 (uu.net). After this change the Internet connection was fast and stable.
If your environment is configured to use 12.127.17.71 as a DNS Server and you're having problems reaching sites on the Internet, consider removing this DNS server from your configuration and use a different ISP's DNS server.