How DNS Works

Kyle Rankin

Director of Engineering Operations

NCC Group Domain Services


Not On Agenda

Host Files: Why DNS was created

In the olden days... (1970s)

Host Files: Why DNS was created

DNS is born (1984)

DNS Today

Root Nameservers

Top Level Domains (TLDs)

Common DNS Setup

External or Internal (or both):

Walk through: Setup

What happens between typing in in a browser and getting back

The Setup:

Walk through: OS to ISP

  1. User to web browser:
  2. web browser to OS:
  3. OS: Hmm not in my hosts file or cache, must ask the nameserver
  4. OS to
  5. Not in my records, I better ask a root nameserver

Walk through: ISP to world

  1. to root:
  2. root to I don't know, ask a net nameserver. Here are their addresses...
  3. to net:
  4. net to No clue, but and know about it. Here are their addresses...
  5. to
  6. to
  7. to OS:
  8. OS to browser:

DNS Caching and TTL

DNS load balacing and failover

Common DNS record types

rDNS: The Internet's caller ID

Fun Exercise

How to take down the Internet

  1. Take out all 13 root DNS servers
  2. There is no second step!
  3. How this works...


Some Useful Resources on DNS