CS440 Computer Networks 1 Domain Name System (DNS) Neil Tang 12/05/2008

CS440 Computer Networks 2 Survey

CS440 Computer Networks 3 Outline  An Example  Basic Concepts  Domain Hierarchy  Name Server  Name Resolution

CS440 Computer Networks 4 An Example

CS440 Computer Networks 5 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 educom princeton ■ ■ ■■ ■ ■ mit csee ux01ux04 physics cisco ■ ■ ■■ ■ ■ yahoonasa ■ ■ ■■ ■ ■ nsfarpa ■ ■ ■■ ■ ■ navyacm ■ ■ ■■ ■ ■ ieee govmilorgnetukfr

CS440 Computer Networks 7 Zone educom princeton ■ ■ ■■ ■ ■ mit csee ux01ux04 physics ciscoyahoonasansfarpanavyacmieee govmilorgnetukfr ■ ■ ■■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■ ■ ■ ■ ■■ ■ ■ 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 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 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, , A, IN) (cisco.com, ns.cisco.com, NS, IN) (ns.cisco.com, , A, IN)  Second level name server (cit.princeton.edu): (cs.princeton.edu, gnat.cs.princeton.edu, NS, IN) (gnat.cs.princeton.edu, , A, IN) (ee.princeton.edu, helios.ee.princeton.edu, NS, IN) (helios.ee.princeton.edu, , A, IN)  Third level name server (gnat.cs.princeton.edu): (cs.princeton.edu, gnat.cs.princeton.edu, MX, IN) (cicada.cs.princeton.edu, , A, IN) (cic.cs.princeton.edu, cicada.cs.princeton.edu, CNAME, IN) (gnat.cs.princeton.edu, , A, IN) ( , A, IN) Information in Name Servers

CS440 Computer Networks 11 Name Resolution