DNS Server 1

8/13/2019 DNS Server 1

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Domain Name Service (DNS)

Configuration in Linux


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DNS Names

DNS is a name resolution method. Invented to overcome the problems with host

files.

Hierarchical distributed database. A domain name is a two (three) tier name.

Administered centrally (eg InterNIC)

Second part is a classification. Eg co

First part identifies the organisation. Eg google


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DNS Names

Last comes the country. Eg in

Also referred to as top level domains (TLD)

DNS consists of thousands of servers.

Each contains its own part of the database.

Example

Hostname = mycomputer

domain = google.co.in


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How DNS Works

Remember, DNS is a hierarchical multilayered name space. Dot (.) character is used as a separator between

levels. Names farthest to the right (com,edu etc) are

known as TLDs.

Used for broad classification. Next are the registered domain names.

Eg google.


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How DNS Works

Once a domain is registered, theorganisation may subdivide it as they see

fit.

Eg ece, cs, atri, csp etc

Few servers handle the TLDs

eg internic Known as root level servers.


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How DNS Works

Once a domain is registered Entries in your DNS zone file tell the servers

how to respond to queries.

Authoritative or non authoritative.


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How DNS Works


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An Example

How an application uses DNS to resolve aname.

Looking up by entering the following in a

browser. http://www.google.co.in/default.html

http states the protocol to be used.

www denotes what?????

Default.html is the required document.


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An Example

3 types of query are involved.

Client makes a recursive query to the local

DNS.

Aniterative

query- takes place between localand other DNS servers

An inverse query. A client provides the IP and

requests the Domain name in a reverse lookup


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Zone Files

Zone files contain the information that tellsthe server how to respond to DNS queries.

Defines the serverszone of authority (SOA).

Standard text file.

Contains records for all nodes that the server is

responsible for.

Zones and domains are NOT the same!

Several servers (zone files) for one domain.


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Zone Files

vi /var/named/chroot/var/named/munivel.com

$TTL 1D

@ IN SOA munivel.com. root.munivel.com. (

4

1D

1H

1W

3H )

@ IN NS ns.munivel.com.

;@ IN MX 10 mail.munivel.com.

ns IN A 192.168.30.5

;manoj IN NS ns.manoj.munivel.com.

www IN A 192.168.30.5

ftp IN CNAME wwwmail IN CNAME www

pub IN CNAME www

man IN CNAME www

myman IN CNAME www

sw500 IN CNAME www


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NS, MX, A And CNAME Records


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Resource records

Different resource records describe the type of

node or service each entry represents. Cname: An alias record.

www CNAME munivel

MX : Mail exchange record. MX 10 mail ; Primary Mail Exchanger

NS : Name Server record. NS ns.munivel.com.

A : A record gw A 192.168.30.5 HINFO mylap TXT "The router"


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Resource Records

Every DNS server must contain a SOA

record.

Always the first entry.

Defines which entry is responsible from thispoint of the hierarchy down.

Identifies: The servername contact email (note the different form of email

address.


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Reverse Lookup Zone

Another type of zone file is the Reverse

Lookup Zone. Note that in an IP address;

Left portion is general.

Right portion is specific.

Used when a client supplies the IP.

Opposite of domain names.

The reverse zone file has reverse addresses.eg. 192.168.30 is entered as 30.168.192.in-addr.arpa All resource records are appended with in-addr.arpa

A holdover from the original ARPAnet.


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vi /var/named/chroot/var/named/munivel.com.rev

$TTL 1D

@ IN SOA 30.168.192.in-addr.arpa. root.munivel.com. (

0 ; serial

1D ; refresh

1H ; retry

1W ; expire

3H ) ; minimum

@ IN NS ns.munivel.com.

5 IN PTR www.munivel.com.

6 IN PTR ftp.munivel.com.

;100 IN PTR www.manoj.munivel.com.

Reverse Lookup Zone


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The SOA Record


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NSLookup Utility

Available on most platforms.(NT,UNIX,Linux etc)

Enables the querying of DNS servers.

Two modes: Batch

Interactive

You will use this in the Lab. A very usefulutility.


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1. bash]# named-checkconf /etc/named.conf

2. bash]# named-checkzone -d munivel.com /var/named/data/munivel.com

Output:

loading munivel.com" from "/var/named/munivel.com" class "IN"zone munivel.com/IN: loaded serial 10

OK

Checking Your Work


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Checking Your Work

1. named-checkzone -d 30.168.192.in-addr.arpa

/var/named/data/munivel.com.rev

Output:

loading 30.168.192.in-addr.arpa" from

"/var/named/data/munivel.com.rev" class "IN"

zone 30.168.192.in-addr.arpa/IN: loaded serial 10

OK


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Starting BIND

[bash]#chkconfig --level 2345 named on

[bash]# /etc/init.d/named restart

[bash]#chkconfig --list named

[bash]#grep named /var/log/messages

(Check the log message)


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Testing The Server

[bash]# dig www.munivel.com

; DiG 9.5.1b2-RedHat-9.5.1-0.8.b2.fc10 www.munivel.com

;; global options: printcmd

;; Got answer:

;; ->>HEADER


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Testing The Server

[bash]# dig munivel.com AXFR 192.168.30.5

; DiG 9.5.1b2-RedHat-9.5.1-0.8.b2.fc10 munivel.com AXFR 192.168.30.5

;; global options: printcmd

munivel.com. 86400 IN SOA munivel.com. root.munivel.com. 4 86400 3600

604800 10800

munivel.com. 86400 IN NS ns.munivel.com.

ftp.munivel.com. 86400 IN CNAME www.munivel.com.

mail.munivel.com. 86400 IN CNAME www.munivel.com.

man.munivel.com. 86400 IN CNAME www.munivel.com.myman.munivel.com. 86400 IN CNAME www.munivel.com.

ns.munivel.com. 86400 IN A 192.168.30.5

praf.munivel.com. 86400 IN CNAME www.munivel.com.

pub.munivel.com. 86400 IN CNAME www.munivel.com.

sw500.munivel.com. 86400 IN CNAME www.munivel.com.

www.munivel.com. 86400 IN A 192.168.30.5munivel.com. 86400 IN SOA munivel.com. root.munivel.com. 4 86400 3600

604800 10800

;; Query time: 0 msec

;; SERVER: 192.168.30.5#53(192.168.30.5)

;; WHEN: Wed Dec 8 15:57:56 2010

;; XFR size: 12 records (messages 1, bytes 291)


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[root@mail ~]# host 192.168.30.5

5.30.168.192.in-addr.arpa domain name pointer www.munivel.com.

Testing The Server


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End of DNS Class

Documents

DNS Server 1