cs440 computer networks 1 domain name system (dns) neil tang 12/05/2008
TRANSCRIPT
CS440 Computer Networks 1
Domain Name System (DNS)Domain Name System (DNS)
Neil TangNeil Tang12/05/200812/05/2008
CS440 Computer Networks 2
SurveySurvey
http://www.cs.montana.edu/survey/
CS440 Computer Networks 3
OutlineOutline
An Example
Basic Concepts
Domain Hierarchy
Name Server
Name Resolution
CS440 Computer Networks 4
An ExampleAn Example
Nameserver
Mailprogram
User
TCP
IP
2cs.princeton.edu
192.12.69.53
user @ cs.princeton.edu1
192.12.69.5 4
192.12.69.5 5
CS440 Computer Networks 5
Basic Concepts Basic Concepts
Name space: the set of possible domain names.
DNS maintains the bindings of name to values (e.g., IP address).
Resolution Mechanism: a procedure which takes a name as the input and returns the corresponding value (e.g., IP address)
Name Server: a program which implements a specific resolution mechanism.
CS440 Computer Networks 6
Domain Hierarchy Domain Hierarchy
edu com
princeton ■ ■ ■ mit
cs ee
ux01 ux04
physics
cisco ■ ■ ■ yahoonasa ■ ■ ■ nsf arpa ■ ■ ■ navy acm ■ ■ ■ ieee
gov mil org net uk fr
CS440 Computer Networks 7
ZoneZone
edu com
princeton■ ■ ■
mit
cs ee
ux01 ux04
physics
cisco yahoonasa nsf arpa navy acm ieee
gov mil org net uk fr
■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■
A domain hierarchy is partitioned to sub-trees called zones, each of
which is usually managed by an administrative Authority.
CS440 Computer Networks 8
Name ServerName Server
The name information contained in each zone is implemented in two or more identical name servers for the sake of redundancy.
Princeton
name server
Cisco
name server
CS
name server
EE
name server■ ■ ■
Root
name server
■ ■ ■
CS440 Computer Networks 9
Information in Name ServersInformation in Name Servers
A set of 5-tuple (Name, Value, Type, Class, TTL) records are maintained in each name server.
Type:
A: the value field gives an IP address.
NS: the value field gives the domain name of a host running the name
server.
CNAME: It is used to define aliases.
MX: the value field gives the domain name for a mail server for the
given domain.
CS440 Computer Networks 10
Root name server: (princeton.edu, cit.princeton.edu, NS, IN) (cit.princeton.edu, 128.196.128.233, A, IN) (cisco.com, ns.cisco.com, NS, IN) (ns.cisco.com, 128.96.32.20, A, IN)
Second level name server (cit.princeton.edu): (cs.princeton.edu, gnat.cs.princeton.edu, NS, IN) (gnat.cs.princeton.edu, 192.12.69.5, A, IN) (ee.princeton.edu, helios.ee.princeton.edu, NS, IN) (helios.ee.princeton.edu, 128.196.28.166, A, IN)
Third level name server (gnat.cs.princeton.edu): (cs.princeton.edu, gnat.cs.princeton.edu, MX, IN) (cicada.cs.princeton.edu, 192.12.69.60, A, IN) (cic.cs.princeton.edu, cicada.cs.princeton.edu, CNAME, IN) (gnat.cs.princeton.edu, 192.12.69.5, A, IN) (www.cs.princeton.edu, 192.12.69.35, A, IN)
Information in Name ServersInformation in Name Servers
CS440 Computer Networks 11
Name ResolutionName Resolution
Rootnameserver
Princetonnameserver
CSnameserver
Localnameserver
1cicada.cs.princeton.edu
192.12.69.608
cicada.cs.princeton.edu
cs.princeton.edu, 192.12.69.5
2
3
4
5
6
7
Client