DNS
Sep 24 2018
*Domain
Name Server*
1)
Requirements:
Master DNS Server -- main.gurukul.com -- 192.168.100.50
Slave DNS Server -- submain.gurukul.com -- 192.168.100.51
Client Machine -- rhcsa.gurukul.com -- 192.168.100.53
2) Installation:
Installation of Bind packages on CentOS7 with below command.
#yum install bind bind-utils
Packages installation on Master and Salve DNS servers are same, so above yum install command will work for both DNS
Servers. bind and bind-utils are main packages required to work for DNS bind configuration. Below packages installed on
my DNS machine.
3) Configure Master DNS:
I hope you know how to configure Single DNS Server, In our earlier post we configured Single DNS machine. Now for
Master DNS Server. we need to edit named.conf file again with some other derivatives.
#vim /etc/named.conf
Change the below things:
options {
listen-on port 53 { 127.0.0.1; 192.168.100.50; };
#listen-on-v6 port 53 { ::1; };
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
allow-query { 192.168.100.51; 192.168.100.50; localhost; };
};
Zone "gurukul.com" IN {
type master;
file "gurukul.com.zone";
also-notify { 192.168.100.51; };
allow-transfer { 192.168.100.51; };
};
Zone "100.168.192.in-addr.arpa" IN {
type master;
file "192.168.100.zone";
also-notify {192.168.100.51;};
allow-transfer {192.168.100.51;};
};
:wq!
listen-on
port 53:
This
derivatives used for every DNS server and important as it would
mentioned on which Internet protocol address (IP address) DNS service
should listen on machine.
Allow-query:
Which
host could allow to Query this DNS server, This derivative could used
in every DNS machines. In Master DNS for security purpose i only used
localhost, own IP and Slave DNS server IP address. Any other then
this can’t query Master DNS server. This way we can isolate Master
DNS server from any attack with LAN.
Also-notify:
This
derivative is only relevant for Master DNS Server. It define Slave
DNS IP address to notify them when Master zone file is reloaded.
Allow-transfer:
This derivative is only relevant for both Master or Slave DNS Server,
this allow defied IP address to allow zone transfer (copy). We can
use this globally or zone specific. The Default behaviour is to allow
zone transfer towards any host, but more friendly and un-secure. It
always suggested to enable transfer towards your slave DNS Server.
Now
we have to build our zones file as we mentioned in named.conf above.
So first work on forward lookup zone file.
4)
Creating Forward lookup Zone:
#vim
/ var/named/gurukul.com.zone
Enter
the below things:
$TTL
86400
@
IN SOA gurukul.com. root.gurukul.com. (
2017092101
; serial (d. adams)
3H
; refresh
15M
; retry
1W
; expiry
1D
) ; minimum
IN
NS main.gurukul.com.
IN
NS submain.gurukul.com.
main.gurukul.com.
IN A 192.168.100.50
submain.gurukul.com.
IN A 192.168.100.51
rhcsa.gurukul.com.
IN A 192.168.100.53
:wq!
5)
Creating
Reverse lookup zone:
Enter
the below things:
$TTL
86400
@
IN SOA gurukul.com. root.gurukul.com. (
2017092101
; Serial
28800
; Refresh
14400
; Retry
3600000
; Expire
86400
) ; Minimum
NS
main.gurukul.com.
NS
submain.gurukul.com.
50
IN PTR main.gurukul.com.
51
IN PTR submain.gurukul.com.
53
IN PTR rhcsa.gurukul.com.
:wq!
6)
#firewall-cmd –-permanent –add-service=dns
7)
#firewall-cmd --reload
8)
#systemctl
restart named
9)
#systemctl enable named
Configuring
Slave DNS Serve
Installation
part of Slave DNS Server is same as of Master DNS Server. Packages
required and installation method is same as of Master DNS Server.
To
configure Slave DNS Server, it need to edit named.conf file of Slave
DNS Server and start named service its should transfer zones file
automatically. Let’s start editing named.conf for Slave DNS Server.
Below is named.conf of Slave DNS Server.
1) #vim /etc/named.conf
Change the below things:
options {
listen-on port 53 { 127.0.0.1; 192.168.100.51; };
#listen-on-v6 port 53 { ::1; };
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
allow-query { 192.168.100.0/24; 127.0.0.1; };
Zone "gurukul.com" IN {
type slave;
masters { 192.168.100.50; };
file "slaves/db.gurukul.com.zone";
};
Zone "100.168.192.in-addr.arpa" IN {
type slave;
masters { 192.168.100.50; };
file "slaves/db.192.168.100.zone";
};
:wq!
In this named.conf, we have some different derivatives than Master DNS. Let study them below.
Allow-query: { 192.168.100.0/24; };
allow-query: This derivative used to query a complete subnet in comparison of Master where we only query for few Host for
security purpose.
type slave;
type: This denote as slave as it used to mention slave zone file
masters {192.168.100.50;};
masters: This derivative is only relevant to Slave DNS as it defines Master DNS IP address of particular zone.
Now we need to start named service, this will transfer zone file from Master towards Slave DNS Server.
2)
#firewall-cmd –-permanent –add-service=dns
3)
#firewall-cmd --reload
4)
#systemctl
restart named
5)
#systemctl enable named
6)
Now
go to cd /var/named/slaves/
#ls
here
you will be found 2 files named:
db.gurukul.com.zone
db.192.168.100.zone
