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Overview of How DNS Works


Centralized design

One server that contains all the mappings (The process of gathering information)

Problems

  • One single point of failure
  • Traffic volume
  • Distant centralized database
  • Maintenance
 

Distributed, Hierarchical Design

Mappings are distributed across a large number of servers organized in a hierarchical fashion

 

Three classes of DNS servers

  1. Root DNS servers
    1. 13 root servers world wide
  2. Top-Level Domain servers
    1. Responsible for top-level domains
      1. .com
      2. .org
      3. .edu
      4. country top-level domains (.uk, .ca)
  3. Authoritative DNS servers
    1. Organizations with publicly accessible hosts
      1. yahoo.com
      2. amazon.com

A 4th type of DNS server is the local DNS server

Each ISP has a local DNS server which acts as a proxy, forwarding a query into the DNS server hierarchy

 
 
 

DNS caching - When a DNS server receives a DNS reply, it can cache the information in the reply in its local memory. Once it has the hostname and IP address cached, it can provide the information to another query, which helps improve the delay performance and reduce the number of DNS messages ricocheting around the Internet.

Cached information is discarded after a set amount of time (normally 2 days)
 


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