The Big Picture for BIND

                        ,-------------------------.
                        | DNS Client Applications |
                        `-------------------------'
       Talks to address(es) listed in /etc/resolv.conf or $DNSCACHEIP
                                     ^|
                                     || queries & responses
                                     || containing complete answers
                                     |v
      ,--(Single giant server process)-----------------------------------.
      | ,--------------------------------------------------------------. |
      | | Cached data                                                  | |
      | `--------------------------------------------------------------' |
      |          |                                           ↑   ↑   ^   |
      |      ,---+---.                                       |   |   |   |
      |      |       ↓                                       |   |   |   |
      |      |    ,--------------------------------------------. |   |   |  Database replication    ,--------------------------.
      |      |    | Local DNS database                         | |   |   |  via "zone transfer"     | Peer content DNS servers |
      |      |    | (i.e. "master", "slave", and "stub" zones) | <================================> |                          |
      |   ,--+--. `--------------------------------------------' |   |   |                          `--------------------------.
      |   |     ↓                                                |   |   |
      |   |   ,----------------------------------------------------. |   |  queries & responses           ,-------------------------.
      |   |   | Query Forwarding                                   | |   |  containing complete answers   | Other proxy DNS servers |
      |   |   | (i.e. "forward" zones and global forwarding)       | <==================================> |                         |
      |   |   `----------------------------------------------------' |   |                                `-------------------------.
      |   v                                                          |   |
      | ,--------------------------------------------------------------. |
      | | Query resolution                                             | |
      | | Primed by data in the "hints" zone for ".".                  | |
      | | Uses data from the cache and the local DNS database.         | |
      | `--------------------------------------------------------------' |
      |         Talks to address(es) listed in the delegations           |
      |                 returned in partial answers                      |
      |                 ↑|           ↑|          ^|                      |
      `-----------------||-----------||----------||----------------------'
                        ||           ||          ||
                        ||           ||          ||
                        |↓           ||          ||        queries & responses
   ,--------(Public IP address)--.   ||          ||        containing possibly partial answers
   | content DNS servers for "." |   ||          ||     (i.e. ending with delegations or aliases)
   `-----------------------------'   ||          ||
      databases contain referrals    ||          ||
            pointing to              |↓          ||
           ,----------(Public IP address)--.     ||
           | content DNS servers for TLDs  |     ||
           | ("com.", "uk.", "moon.", &c.) |     ||
           `-------------------------------'     ||
                  databases contain referrals    ||
                       pointing to               |v
                         ,------------(Public IP address)---------.
                         | content DNS servers for 2LDs and below |
                         `----------------------------------------'