Post on 03-Jun-2018
8/13/2019 DNS Server 1
1/25
Domain Name Service (DNS)
Configuration in Linux
8/13/2019 DNS Server 1
2/25
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
8/13/2019 DNS Server 1
3/25
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
8/13/2019 DNS Server 1
4/25
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.
8/13/2019 DNS Server 1
5/25
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.
8/13/2019 DNS Server 1
6/25
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.
8/13/2019 DNS Server 1
7/25
How DNS Works
8/13/2019 DNS Server 1
8/25
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.
8/13/2019 DNS Server 1
9/25
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
8/13/2019 DNS Server 1
10/25
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.
8/13/2019 DNS Server 1
11/25
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
8/13/2019 DNS Server 1
12/25
NS, MX, A And CNAME Records
8/13/2019 DNS Server 1
13/25
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"
8/13/2019 DNS Server 1
14/25
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.
8/13/2019 DNS Server 1
15/25
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.
8/13/2019 DNS Server 1
16/25
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
8/13/2019 DNS Server 1
17/25
The SOA Record
8/13/2019 DNS Server 1
18/25
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.
8/13/2019 DNS Server 1
19/25
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
8/13/2019 DNS Server 1
20/25
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
8/13/2019 DNS Server 1
21/25
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)
8/13/2019 DNS Server 1
22/25
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
8/13/2019 DNS Server 1
23/25
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)
8/13/2019 DNS Server 1
24/25
[root@mail ~]# host 192.168.30.5
5.30.168.192.in-addr.arpa domain name pointer www.munivel.com.
Testing The Server
8/13/2019 DNS Server 1
25/25
End of DNS Class