====== DNS ======

There are three classes of DNS servers:
  - Root DNS servers
    - There are more than 2000 root servers world wide. They are copies of 13 different root servers
  - Top Level Domain DNS servers
  - Authoritative DNS servers


Finding authoritative DNS servers:
<code bash>
dig NS apple.com +short  # the NS record identifies which servers are supposed to be authoritative;
                         # querying those servers directly and checking for aa confirms they actually are
</code>

===== Resource Records =====

Resource record is a four-tuple - **(Name, Value, Type, TTL)** 
  * TTL determines when the resource should be removed from the cache
  * Type **A**:
    * ''Name'' is the hostname
    * ''Value'' is the IP address