Transcript Domain Name System (DNS) - Eastern Michigan University

Domain Name System (DNS)
Network Information Center (NIC) :
HOSTS.TXT
DNS -Hierarchical Namespace
(Root)
mil
Pentagon
edu
emich
cislab
gov
umich
White
house
com
ibm
yahoo
Fully Qualified Domain Names
& Domains
Ends with a “DOT”
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cispdc.cislab.emich.edu.
www.yahoo.com
mail.emich.edu
Generic Domain
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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
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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
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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 space
Zones of Authority (Zones)
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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 Process
User issues gethostbyname() /
gethostbyaddr() request
Resolver formulates a query to NS
NS check local authoritative DB or
cache first and return. Otherwise, check
one of 13 root Name Servers or as high
as possible
Return to user program with
corresponding IP address, host name,
or error message
Resolver Operation
Two types of queries
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Recursive: find the answer all the way
through all the name server
Non-Recursive: list name server references
Two types of responses
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Authoritative: request for a domain in a
zone over its authority
Non-authoritative:
Domain Name Server Operation
Primary NS:
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Loads a zone’s information from disk, and
has authority over the zone
Secondary NS:
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Has authority over the zone but obtains the
zone information from primary NS using a
process call ZONE TRANSFER
Caching-only:
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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
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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
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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 zone
type 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
1
SOA ns.linux.net. (
1 ; Serial
8H ; Refresh
2H ; Retry
4W ; Expire
1D) ; Minimum TTL
NS ns.linux.net.
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
192.168.196.5
web
CNAME
www
pz/192.168.196 file
$TTL 3D
@ IN SOA ns.linux.net.(
199802151; 8H ;2H ;4W ;1D) ;
NS
ns.linux.net.
2
4
5
PTR
PTR
PTR
ns.linux.net.
mail.linux.net.
www.linux.net.