DNS some keywords

1. Name servers host a domain’s DNS information in a text file called the zone file. They’re are also known as **Servers of
   Authority (SOAs)**
2. On Linux (and probably most Unix), there is no OS-level DNS caching unless nscd is installed and running. Even then, the DNS caching feature of nscd is disabled by default at least in Debian because it's broken. The practical upshot is that your linux system very very probably does not do any OS-level DNS caching.
3. An AAAA record is just like an A record, but for IPv6 IP addresses. A typical AAAA record looks like the following:

参考 https://www.linode.com/docs/networking/dns/dns-records-an-introduction