Domain Name System DNS - PowerPoint PPT Presentation

1 / 23
About This Presentation

Domain Name System DNS


Domain Name Space continued ... The domain name of a node is the list of the labels on the path from the node to ... Domain Name Servers. Servers are organized ... – PowerPoint PPT presentation

Number of Views:348
Avg rating:3.0/5.0
Slides: 24
Provided by: jarettbo
Tags: dns | domain | name | names | system


Transcript and Presenter's Notes

Title: Domain Name System DNS

Domain Name System(DNS?)
  • By
  • Jarett Boxberger

First, Some History
  • Before DNS
  • One computer was used as a host that knew all
  • Table had to be updated by Stanford
  • Others hosts then downloaded updated tables
  • System worked well for finding computers, problem
    revolved around the updates

DNS to the Rescue
  • 1984, Paul Mockapetris designed DNS
  • No one organization responsible for updating the
  • Known as a distributed database, no one server
    stores all the information
  • DNS allows for almost unlimited growth

How does DNS Work?
  • DNS makes remembering Web Addresses much easier
  • Which is easier to remember

Domain Name Space
  • Each node represents a domain, and everything
    below that node is in its domain
  • Domains are broken down into

Domain Name Space continued
  • There are also 2 letter codes that represent
    countries, these are defined as country or
    geographic domains
  • They are defined in ISO 3166

  • Each has a label, which is 0-63 octets in length
  • The domain name of a node is the list of the
    labels on the path from the node to the root of
    the tree
  • Labels are read from left to right, or from the
    most specific, farthest from the root, to the
    least specific, closest to the root.

Nodes Tree
Domain Name Servers
  • Servers are organized in a hierarchy
  • Each server has an authority over a part of the
    naming hierarchy
  • Each server does not keep all names
  • Needs to know other servers who are responsible
    for the other subdomains

Servers cont.
  • The authority server, has the name to address
    translation table, and either is able to answer a
    query, or knows the server that does
  • A server can serve more than one domain
  • The root server knows about the servers for the
    top-level domains
  • Each server knows the root server

Server Types
  • Root Severs
  • Ultimate authority
  • 1 primary, backed by 12 secondary
  • Primary Severs
  • Has authority over a zone.
  • Secondary Servers
  • Back up Primary Servers
  • Caching Servers
  • Not authoritative for any domain
  • Answers queries by asking other authoritative
    servers, then storing that information in cache
  • Used to relieve burden of authoritative servers
  • Slave Servers
  • Can function as primary, or secondary servers.
  • Have no contact with servers outside the

Server Hierarchy
Updating Tables
  • When new hosts are added to a zone, the
    administrator adds the name and IP address to
    file, called a record.
  • Primary name server is then notified, and it
    updates its tables.
  • Secondary hosts query the primary on a regular
    basis, usually every 3 hours.

DNS Records
  • A records Given a domain name, return its IP
  • PTR records Given an IP address, return the
    corresponding domain name
  • HINFO and TXT records Given a domain name,
    return descriptive information

  • Two types
  • Recursive Give me an answer
  • Done by your computer to a resolver
  • Iterative Give me an answer or a referral to the
    next server
  • Done by the resolver to the name servers

How Queries get answered
  • Programs interact with the DNS servers through
    resolvers, which answers the query, or queries
    other hosts
  • Message formats are specified in RCF 1035
  • Queries and responses can be done either by TCP
    or UDP

The Process
DNS Message Format
  • Identification is set by the client and returned
    by the server
  • Flags provide additional information about the
  • Number of the total number of entries in the
    corresponding sections
  • Questions section contains the query
  • Answer, Authority, Additional Information
    sections consist of a set of resource records,
    which is the answer to the query. Each record
    describes one name.

Sent by your computer to the resolver.
Query Reply RR Fields
  • Domain name is the query name from the query.
  • Type type of information
  • Class is 1 for Internet domain
  • Time to live is the time the information can be
    cached, expressed in seconds.
  • Resource data length is the number of bytes of
    resource data

Sent by the server to your computer.
Query Types
  • Servers respond to a full name only
  • What happens when we give a partial address?
  • Resolvers try and fill in the rest
  • Try various suffixes
  • Example You entered www.fhsu
  • The resolver would try putting different suffixes
    on, like .com .edu .gov ect.
  • If that doesnt work an error is displayed

Types of DNS Entries
  • DNS is not just used for name to address
  • Also used for finding mail servers, and pop

  • DNS makes remembering web addresses much easier
    by mapping names to addresses
  • Names are hierarchical
  • No one computer contains all information
  • Tables are exchanged between servers to keep the
    information up-to-date
Write a Comment
User Comments (0)