dns. introduction what is dns? –hierarchy or tree –dot used as a separator
TRANSCRIPT
DNS
Introduction
• What is DNS? – Hierarchy or Tree– Dot used as a separator
Top-level domain
Domain Name MeaningCOM Commercial organizationsEDU Educational institutionsGOV Government institutionsMIL Military groupsNET Major network support ORG Organizations other than those aboveARPA Temporary ARPANET domainINT International organizationscountry codeEach country (geographical scheme)
zone
• Domain Delegation
Primary (Master) Name Server– Contains the writable authoritative copy for th
e zones
Secondary (Slave) Name Server– Contains mirror copy of the data from a
primary nameserver
Introduction to DNS
• DNS Clients – /etc/resolv.conf
• Authoritative DNS Servers – provide the information for your DNS domain
• Caching DNS Server – Most servers don’t ask authoritative servers
for DNS directly – ask a caching DNS server
How Does It Work?
• Listens at UDP and TCP port 53 – UDP for routine queries – TCP used for zone transfers
Basic DNS Testing of DNS Resolution
• The Host Command– host www.google.com
• The nslookup Command– nslookup www.google.com– nslookup
The /etc/resolv.conf File
• Nameserver– IP address of your DNS nameserver
• Search
• Domain– localdomain use by default
search my-site.com my-site.net my-site.org
nameserver 192.168.1.100
nameserver 192.168.1.102
BIND
• Downloading and Installing the BIND
How To Get BIND Started
• service named start
• service named stop
• service named restart
DNS File Locations
• named.conf– /etc/named.conf
• zone files– /var/named
Named.conf
• This file usually has two zone areas: – Forward zone file – Reverse zone file
Forward zone file
zone "my-site.com" { type master;
file "my-site.zone";
};
Reverse zone file
zone "1.168.192.in-addr.arpa" { type master;
notify no;
file "192-168-1.zone";
};
Configuring The Zone Files
• By default located in the directory /var/named
• Each zone file contains a variety of records (SOA, NS, MX, A, and CNAME)
Time to Live Value
– D signifies days– W signifies weeks– H signifies hours
$TTL 3D
Standard Resource Records
• SOA– Start of Authority, Marks the begining of a zon
e's data
• NS – IP address or CNAME of the name server
• A– IP address of server
• MX– Mail server DNS name
• CNAME– Server name alias
• PTR– Last octet of server's IP address
The SOA Record
• FormatName Class Type Name-Server Email-Address Serial-No Refresh
Retry Expiry Minimum-TTL
@ IN SOA ns1.my-site.com. hostmaster.my-site.com. ( 2004100801 ; serial #
4H ; refresh
1H ; retry
1W ; expiry
1D ) ; minimum
the general format:
Name Class Type Data
eeunix IN A 130.111.148.45
IN MX 0 eeunix
IN MX 1 maine.maine.edu.
Trouble Shoot
• Domain cmu.ac.th– ns.cmu.ac.th
• Domain Delegation – eng.cmu.ac.th
• แก้�/เพิ่��ม work ?
• Transfer zone ?