DDNS

In order to figure out what's DNS and how it work, I would Implement Dynamic DNS server in User-level.

What's the difference of DNS and DDNS?

DNS server uses master file to record the mapping relationship of Domain Name and IP. The master file is just a text file, and lack of flexibility to change the mapping. That's why DDNS server comes.DDNS server extends MESSAGE format(is used to query) to support that dynamically modify the master file.

Standard Reference:

• rfc1033
• rfc1034
• rfc1035
• rfc2136

Name Server Architecture:

                 Local Host                        |  Foreign
                                                   |
      +---------+                                  |
     /         /|                                  |
    +---------+ |             +----------+         |  +--------+
    |         | |             |          |responses|  |        |
    |         | |             |   Name   |---------|->|Foreign |
    |  Master |-------------->|  Server  |         |  |Resolver|
    |  files  | |             |          |<--------|--|        |
    |         |/              |          | queries |  +--------+
    +---------+               +----------+         |

Resolver Architecture:

                 Local Host                        |  Foreign
                                                   |
    +---------+               +----------+         |  +--------+
    |         | user queries  |          |queries  |  |        |
    |  User   |-------------->|          |---------|->|Foreign |
    | Program |               | Resolver |         |  |  Name  |
    |         |<--------------|          |<--------|--| Server |
    |         | user responses|          |responses|  |        |
    +---------+               +----------+         |  +--------+
                                |     A            |
                cache additions |     | references |
                                V     |            |
                              +----------+         |
                              |  cache   |         |
                              +----------+         |

Future Architecture:

                 Local Host                        |  Foreign
                                                   |
    +---------+               +----------+         |  +--------+
    |         | user queries  |          |queries  |  |        |
    |  User   |-------------->|          |---------|->|Foreign |
    | Program |               | Resolver |         |  |  Name  |
    |         |<--------------|          |<--------|--| Server |
    |         | user responses|          |responses|  |        |
    +---------+               +----------+         |  +--------+
                                |     A            |
                cache additions |     | references |
                                V     |            |
                              +----------+         |
                              |  Shared  |         |
                              | database |         |
                              +----------+         |
                                A     |            |
      +---------+     refreshes |     | references |
     /         /|               |     V            |
    +---------+ |             +----------+         |  +--------+
    |         | |             |          |responses|  |        |
    |         | |             |   Name   |---------|->|Foreign |
    |  Master |-------------->|  Server  |         |  |Resolver|
    |  files  | |             |          |<--------|--|        |
    |         |/              |          | queries |  +--------+
    +---------+               +----------+         |
                                A     |maintenance |  +--------+
                                |     +------------|->|        |
                                |      queries     |  |Foreign |
                                |                  |  |  Name  |
                                +------------------|--| Server |
                             maintenance responses |  +--------+