Domain Name Resolution

1
Domain Name Resolution
Joshua Erdman Digital-Foundation.net
2
DNS Background

• What is a domain name?
• Familiar, easy to remember names for computers on
  the Internet (such as internic.net).
• Correspond to a series of numbers (called
  Internet Protocol numbers, AKA IP addresses) that
  serve as routing addresses on the Internet.
• Domain names are used generally as a convenient
  way of locating information and reaching others
  on the Internet.

3
DNS Background
What does it mean to "register" a domain
name? The Internet domain name system (DNS)
consists of a directory, organized
hierarchically, of all the domain names and their
corresponding computers registered to particular
companies and persons using the Internet. When
you register a domain name, it will be associated
with the computer on the Internet you designate
during the period the registration is in effect.
Taken from ICANN.com
4
So what is DNS Resolution?
DNS Resolution is the procedure used to resolve a
IP address from a domain name.   This is very
similar to how we get the phone number of a
person we want to contact.   It is all based on
hierarchy.
5
DNS Resolution analogy

• Looking up a phone number
• Get the phone book of the right city
• People are listed by last name
• Then narrow it down to a first name.
• It is the phone number that allows you to
  communicate over the phone, not the persons
  name.

6
DNS Foundation
All computers communicate by addressing each
other using IP addresses.   So every time you try
to connect to a website, or send an e-mail, DNS
resolution is occurring. Just like phone numbers,
multiple domain names can resolve to the same IP
address.
7
Domain Names vs. URLs
A domain name is contained in a URL. See the
examples below. ftp//ftp.company.com/download
s.report.doc http//www.networkclue.com/index.php
8
DNS Resolution Scenario
5 components
http//www.google.com
9
Domain Name Table
10
WHOIS DB
11
GTLD History
ICANNInternet Consortium for Assigned Names and
Numbers
Internic
Domain Registrars
Godaddy.com
Register.com
Net Sol
12
Registrars

• Benefits
• Price Wars
• Features (e-mail, web hosting, advertising, etc.)
• Easier to register domains

• Problems
• Long distance wars
• ISPs using 1 registrar
• Customers registering because it is now so simple

13
IP Address Registration
ICANNInternet Consortium for Assigned Names and
Numbers
IP Registrars
ARPNIC Asia Pacific Registry
RIPEEuropean Registry
ARIN American Registry for Internet Numbers
14
Reverse DNS Resolution
Reverse DNS Resolution is the procedure used to
resolve a domain name from an IP
address.  Recall Multiple domain names can
resolve to an IP address (just like multiple
people can have the same phone number). It is
the ISPs responsibility to maintain reverse DNS
tables.
15
Reverse DNS Resolution
Internet
4 components
4.3.2.1.in-addr.arpa
16
Reverse DNS Resolution

• How is Reverse DNS this useful?
• Tracing traffic that goes through Firewalls
• Documentation
• E-mail server validation

17
Questions Answers
18
(No Transcript)