Overview

• Similar to ARP in the fact that it is a resolution protocol
• All it does is map a url to an ip address
• Name Space: Every named machine/device must be unique
• Name space can be flat or hierarchical

Why?

• Internet is massive so we need an easy way to connect do different networks
• We cant remember a ip for each website, we use WORDS as people.

How it works

• You enter an address into your web browser
• Your request goes into your file transfer client and sends it over to your DNS client
• Then your DNS client will send a query to its closest DNS server
• The DNS server then sends a response back to your DNS client which then moves the requested IP to your file transfer client
• AND THEN your application now has your requested IP address and can go and find the site

Hierarchical Domain Name Space

• Root - there are 13 root server operators
  • arpa, com, edu, org, ad, zw, etc
    • Another site
      • Another layer of site
        • It can keep on going

Fully Qualified Domain Name (FQDN)

• FQDN is the domain name that contains the host name -> has a unique address
• Example:
  • Root
    • .edu
      • fhda.edu
        • atc.fhda.edu
          • challeneger.atc.fhda.edu This is the FQDN

DNS Servers and Domains

• A domain is a sub-tree of the domain name space
• Every domain needs to have at least one server configured ti provide a name
• More than one name server will boost performance and protect against single point failures
• There is a minimum knowledge needed by the DNS players to keep it going
  • The parent can only see the child namespace. So only EDU can see root but EDU’s child cannot see ROOT. They all only know the namespace below them
• IP addresses for DNS servers dont need to be local, but it is generally assigned by your ISP

DNS Organization - finish later

• Sponsored gTLDs
  • AERO, ASIA, CAT, EDU, JOBS, XXX, GOV

Authoritative or Not

• Name servers have 2 different types of answers
  • Authoritative
    • This is a response when you actually get the IP from a DNS server.
  • Non Authoritative
    • This is where you get the IP from a cache. Sites that have been visited before will auto cache the IP address. Your computer remembers.

DNS Messages

• DNS has two types of messages
  • Query
    • Consists of a header and question records
  • Response
    • consists of a header, question records, answer section, authoritative section and additional section