1. Student name:
hazem al maliki
DNS
Domain Name Systems

2. 2
Domain Name System
 DNS Overview
 DNS Zones
 Forward
 Reverse
 Fowarding
 DNS Delegation/Parenting
 Mail Exchangers

3. 3
Overview
 On the Internet, the Domain Name System (DNS)
associates various sorts of information with
domain names
 Serves as the "phone book" for the Internet
 Translates human-readable computer hostnames into
IP addresses
 Required bynetworking equipment to delivering information
 Also stores other information
 Such as the list of mail exchange servers that accept email for
a given domain.
 By providing a worldwide keyword-based redirection
service, the Domain Name System is an essential
component of the modern Internet

4. 4
Uses
 The most basic use of DNS is to
translate hostnames to IP addresses.
 Very much like a phone book
 For example, what is the internet address
of en.wikipedia.org?
 The Domain Name System can be used to tell
you it is 66.230.200.100

5. 5
Uses
 DNS also has other important uses
 DNS makes it possible
 Assign Internet destinations to the human organization or
concern they represent
 Independent of the physical routing hierarchy represented by
the numerical

6. 6
How DNS works

7. 7
How DNS Works - Theory
 Domain names
 Arranged in a tree
 Cut into zones
 Each served by a
nameserver

8. 8
How DNS Works - Theory
 The domain name space consists of a tree of
domain names.
 Each node or leaf in the tree has one or more
resource records, which hold information
associated with the domain name.
 The tree sub-divides into zones.
 A zone consists of a collection of connected nodes
authoritatively served by an authoritative DNS
nameserver.
 Note that a single nameserver can host several zones

9. 9
How DNS Works - Theory
 When a system administrator wants to let
another administrator control a part of the
domain name space within his or her zone of
authority
 Can delegate control to the other administrator.
 Splits a part of the old zone off into a new zone
 Comes under the authority of the second administrator's
nameservers
 The old zone becomes no longer authoritative for
what goes under the authority of the new zone.

10. 10
Types of DNS records
 Important categories of data stored in DNS include the following:
 An A record or address record maps a hostname to a 32-bit IPv4 address.
 An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6
address.
 A CNAME record or canonical name record is an alias of one name to another
 The A record to which the alias points can be either local or remote - on a foreign name server.
 This is useful when running multiple services (like an FTP and a webserver) from a single IP
address.
 Each service can then have its own entry in DNS (like ftp.example.com. and
www.example.com.)
 An MX record or mail exchange record maps a domain name to a list of
mail exchange servers for that domain.
 A PTR record or pointer record maps an IPv4 address to the canonical name for
that host.
 Setting up a PTR record for a hostname in the in-addr.arpa. domain that corresponds to an IP
address implements reverse DNS lookup for that address.
 For example (at the time of writing), www.icann.net has the IP address 192.0.34.164, but a
PTR record maps 164.34.0.192.in-addr.arpa to its canonical name, referrals.icann.org.
 An NS record or name server record maps a domain name to a list of DNS
servers authoritative for that domain.
 Delegations depend on NS records.

11. 11
DNS Zones
Forward

12. 12
DNS Reverse Lookup
 Overview
 Typically, the Domain Name System is used to
determine what IP address is associated with a
given domain name.
 So, to reverse-resolve a known IP address is to
look up what the associated domain name is
belonging to that IP address.
 A reverse lookup is often referred to as reverse
resolving, or more specifically reverse DNS
lookup, and is accomplished using a "reverse IN-ADDR
entry" in the form of a PTR record

13. 13
 Forward DNS lookup
 Forward DNS lookup is using an Internet
domain name to find an IP address.
 Reverse DNS lookup
 Reverse DNS lookup is using an Internet
IP address to find a domain name.

14. 14
DNS Zones
Forwarding

15. 15
DNS Forwarding
 In large, well organized, academic or ISP networks you will
sometimes find that the network people have set up a forwarder
hierarchy of DNS servers
 Helps lighten the internal network load and the load on the outside
servers
 It's not easy to know if you're inside such a network or not
 By using the DNS server of your network provider as a
”forwarder”' you can make the responses to queries faster and
less of a load on your network
 Your nameserver forwards queries to your ISP nameserver
 Each time this happens you will dip into the big cache of your
ISPs nameserver
 Thus speeding your queries up, your nameserver does not have to
do all the work itself
 If you use a modem this can be quite a win
http://tldp.org/HOWTO/DNS-HOWTO-4.html

16. 16
Mail Exchangers
Covered in previous section:
How DNS Works In Practice
- Other Applications