Domain Name System (DNS)

Network Information Center (NIC) : HOSTS.TXT

DNS -- Hierarchical Namespace

(Root)

edumil gov com

Pentagon emich umich Whitehouse

ibm yahoo

cislab

Fully Qualified Domain Names

& Domains

Ends with a “DOT” cispdc.cislab.emich.e

du. www.yahoo.com mail.emich.edu

Generic Domain See right side >>

Domain Name

Meaning

com Commerical

edu Educational

gov Government

int International

mil U.S Military

net Major Network

org Non-profit

Country code ISO 2-letter

Mapping Domain Names to IP Address Name Server: Holds name-to-address

database or point to other who does Name Resolver: Answer requests from

the client

Mapping IP Address to Domain Names Pointer Query: A domain name query to

find the host name associated with an IP addresss Using reverse lookup 129.34.139.30= 139.34.129.in-addr.arpa

Distributed name spaceZones of Authority (Zones) Group of Symbolic Domain Name In each of these zones, on or more hosts

maintains a database of names and IP mapping table

These local name servers are interconnected into a hierarchical tree of domain

Each zone contains a part or sub-tree of the hierarchical tree of the domain

Authority of a zone: Name server in the zone Delegate authority: Superior domain name

server

Resolution ProcessUser issues gethostbyname() / gethostbyaddr() requestResolver formulates a query to NSNS check local authoritative DB or cache first and return. Otherwise, check one of 13 root Name Servers or as high as possibleReturn to user program with corresponding IP address, host name, or error message

Resolver Operation

Two types of queries Recursive: find the answer all the way

through all the name server Non-Recursive: list name server

references

Two types of responses Authoritative: request for a domain in

a zone over its authority Non-authoritative:

Domain Name Server Operation

Primary NS: Loads a zone’s information from disk,

and has authority over the zone

Secondary NS: Has authority over the zone but

obtains the zone information from primary NS using a process call ZONE TRANSFER

Caching-only: No authority for any zone but obtain

all info. and cache it in memory

DNS Distributed database record format

DNS Resource Record (RR): it provides a mapping between domain names and host IP addresses

General Format Name: Domain Name to be defined TTL: Time-To-Live in second Class: protocol family usually IN

(internet) Type: Type of resource (see next page) Rdata: Depends on the type

DNS Distributed database record format

Resource Record Type and Rdata Start of Authority (SOA) = full NS name Name Server (NS) = Host name Domain Name Pointer (PTR) = Domain

name Canonical Name (CNAME) = Domain

name Mail Exchange (MX) = value and host

name Host Address (A) = 32 bit IP address

BIND DNS Server named.conf file

zone "0.0.127.in-addr.arpa" { ;loopback zonetype master; file "pz/127.0.0"; };

zone "linux.net" {;forward Zone type master; file "pz/linux.net"; };

zone "196.168.192.in-addr.arpa" {;Reverse Zone

type master; file "pz/192.168.196"; };

pz/127.0.0 File$TTL 3D @ IN SOA ns.linux.net. (

1 ; Serial 8H ; Refresh 2H ; Retry 4W ; Expire 1D) ; Minimum TTL

NS ns.linux.net. 1 PTR localhost.

pz/linux.net file$TTL 3D @ IN SOA ns.linux.net. (

199802151 ; 8H ; 2H; 4W; 1D )NS ns ; name server MX 10 mail ; Primary Mail

localhost A 127.0.0.1 ns A 192.168.196.2 mail A 192.168.196.4 www A 192.168.196.5web CNAME www

pz/192.168.196 file

$TTL 3D @ IN SOA ns.linux.net.( 199802151; 8H ;2H ;4W ;1D) ;

NS ns.linux.net. 2 PTR ns.linux.net. 4 PTR mail.linux.net. 5 PTR www.linux.net.