Built in NTP server addresses?

While monitoring NTP with Wireshark, I could see requests going out to the Internet, as well as to my local server.  However, only my local server has been configured for use.  Why is it going out to the net?  Are there built in server names? Here are a couple of examples: jknott@linux:~> host 209.115.181.106 106.181.115.209.in-addr.arpa domain name pointer mirrors.switch.ca. jknott@linux:~> host 2606:4700:f1::123 3.2.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.f.0.0.0.0.7.4.6.0.6.2.ip6.arpa domain name pointer time.cloudflare.com. I have never configured those servers on anything I've worked on. I'm running Leap 15.3.