Setup DNS-Server on centOS-7 (Master-Slave mode)

Setup Primary (Master) DNS Server

Install bind9 packages on your server. Run the following command:

“yum install bind bind-utils -y”

1. Configure DNS Server

Edit ‘/etc/named.conf’ file.

vi /etc/named.conf

Add the lines as shown in bold:

//
// named.conf
//
// Provided by Red Hat bind package to configure the ISC BIND named(8) DNS
// server as a caching only nameserver (as a localhost DNS resolver only).
//
// See /usr/share/doc/bind*/sample/ for example named configuration files.
//

options {
    listen-on port 53 { 127.0.0.1; [Master-dns ip];}; ### Master DNS IP ###
#    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     { localhost; 192.168.1.0/24;}; ### IP Range ###
    allow-transfer{ localhost; [slave-dns ip]; };   ### Slave DNS IP ###

    /* 
     - If you are building an AUTHORITATIVE DNS server, do NOT enable recursion.
     - If you are building a RECURSIVE (caching) DNS server, you need to enable 
       recursion. 
     - If your recursive DNS server has a public IP address, you MUST enable access 
       control to limit queries to your legitimate users. Failing to do so will
       cause your server to become part of large scale DNS amplification 
       attacks. Implementing BCP38 within your network would greatly
       reduce such attack surface 
    */
    recursion yes;

    dnssec-enable yes;
    dnssec-validation yes;
    dnssec-lookaside auto;

    /* Path to ISC DLV key */
    bindkeys-file "/etc/named.iscdlv.key";

    managed-keys-directory "/var/named/dynamic";

    pid-file "/run/named/named.pid";
    session-keyfile "/run/named/session.key";
};

logging {
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };
};

zone "." IN {
    type hint;
    file "named.ca";
};

zone "learnwithak.local" IN { 

type master; 

file "forward.learnwithak"; 

allow-update { none; }; 

}; 

include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";

2 Create Forward Zone

Create forward.learnwithak file in the ‘/var/named’ directory.

vi /var/named/forward.learnwithak

Add the following lines:

$TTL 86400
@ IN SOA ehs-dns-master.learnwithak.local. root.learnwithak.local. (
 2011071001 ;Serial
 3600 ;Refresh
 1800 ;Retry
 604800 ;Expire
 86400 ;Minimum TTL
)
@ IN NS ehs-dns-master.lernwithak.local.
@ IN NS ehs-dns-slave.learnwithak.local.
@ IN A 172.16.4.10
@ IN A 172.16.4.11
@ IN A 172.16.4.9
@ IN A 172.16.4.8
@ IN A 172.16.4.7
@ IN A 172.16.4.6
@ IN A 172.16.4.5
@ IN A 172.16.4.4
@ IN A 172.16.5.2
@ IN A 172.16.5.3
@ IN A 172.16.5.4
ehs-dns-master  IN A 172.16.4.10
ehs-dns-standby IN A 172.16.4.11
ehs-api-2       IN A 172.16.4.9
ehs-api-1       IN A 172.16.4.8
ehs-api-lb      IN A 172.16.4.7
ehs-api-orchestration IN A 172.16.4.6
rabbit-standby  IN A 172.16.4.5
rabbit-master   IN A 172.16.4.4
db-slave        IN A 172.16.5.2
db-master       IN A 172.16.5.3
ehs-ldap        IN A 172.16.5.4

3. Start the DNS service

Enable and start DNS service:

systemctl enable named
systemctl start named

4. Firewall Configuration

We must allow the DNS service default port 53 through firewall.

Add the following lines in /etc/sysconfig/iptables

-A INPUT -p tcp -m state --state NEW -m tcp --dport 53 -j ACCEPT
-A INPUT -p udp -m state --state NEW -m udp --dport 53 -j ACCEPT

5. Restart Firewall

Run the following command

sudo systemctl restart iptables

6. Configuring Permissions, Ownership, and SELinux

Run the following commands one by one:

chgrp named -R /var/named
chown -v root:named /etc/named.conf
restorecon -rv /var/named
restorecon /etc/named.conf

7. Test DNS configuration and zone files for any syntax errors

Check DNS default configuration file:

named-checkconf /etc/named.conf

If it returns nothing, your configuration file is valid.

Check Forward zone:

named-checkzone learnwithak.local /var/named/forward.learnwithak

Sample output:

zone learnwithak.local/IN: loaded serial 2011071001
OK

Add the DNS Server details in your network interface config file.

vi /etc/sysconfig/network-scripts/ifcfg-ens160

HWADDR=00:50:56:01:04:20
NAME=ens160
GATEWAY=172.16.4.1
DNS=172.16.4.10
DEVICE=ens160
ONBOOT=yes
USERCTL=no
BOOTPROTO=static
NETMASK=255.255.255.0
IPADDR=172.16.4.10
PEERDNS=yes

check_link_down() {
 return 1;
}

Edit file /etc/resolv.conf,

vi /etc/resolv.conf

Add the name server ip address:

nameserver    172.16.4.10

Save and close the file.

Restart network service:

systemctl restart network

8. Test DNS Server

dig ehs-dns-master.learnwithak.local

Sample Output:

; <<>> DiG 9.9.4-RedHat-9.9.4-38.el7_3.1 <<>> ehs-dns-master.learnwithak.local
;; global options: +cmd
;; Got answer:
;; ->>HEADER<

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;ehs-dns-master.learnwithak.local. IN A

;; ANSWER SECTION:
ehs-dns-master.learnwithak.local. 86400 IN A 172.16.4.10

;; AUTHORITY SECTION:
learnwithak.local. 86400 IN NS ehs-dns-master.learnwithak.local.
learnwithak.local. 86400 IN NS ehs-dns-standby.learnwithak.local.

;; ADDITIONAL SECTION:
ehs-dns-standby.learnwithak.local. 86400 IN A 172.16.4.11

;; Query time: 0 msec
;; SERVER: 172.16.4.10#53(172.16.4.10)
;; WHEN: Wed Feb 22 13:15:23 UTC 2017
;; MSG SIZE rcvd: 138

Server: 172.16.4.10
Address: 172.16.4.10#53

nslookup learnwithak.local

Sample Output:

Name: learnwithak.local
Address: 172.16.4.11
Name: learnwithak.local
Address: 172.16.5.4
Name: learnwithak.local
Address: 172.16.4.9
Name: learnwithak.local
Address: 172.16.5.2
Name: learnwithak.local
Address: 172.16.4.7
Name: learnwithak.local
Address: 172.16.4.4
Name: learnwithak.local
Address: 172.16.5.3
Name: learnwithak.local
Address: 172.16.4.8
Name: learnwithak.local
Address: 172.16.4.5
Name: learnwithak.local
Address: 172.16.4.6
Name: learnwithak.local
Address: 172.16.4.10

Now the Primary DNS server is ready to use.

It is time to configure our Secondary DNS server.

Setup Secondary(Slave) DNS Server

Install bind packages using the following command:

yum install bind bind-utils -y

1. Configure Slave DNS Server

Edit file ‘/etc/named.conf’:

vi /etc/named.conf

Make the changes as shown in bold.

//
// named.conf
//
// Provided by Red Hat bind package to configure the ISC BIND named(8) DNS
// server as a caching only nameserver (as a localhost DNS resolver only).
//
// See /usr/share/doc/bind*/sample/ for example named configuration files.
//
options {
listen-on port 53 { 127.0.0.1; 172.16.4.11; };
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     { localhost; 172.16.4.0/24; };
.
.
.
.
zone "." IN {
type hint;
file "named.ca";
};
zone "learnwithak.local" IN { 

type slave; 

file "slaves/learnwithak.fwd"; 

masters { 172.16.4.10; }; 

}; 

include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";

 

2. Start the DNS Service

systemctl enable named
systemctl start named

Now the forward  zone is automatically replicated from Master DNS server to ‘/var/named/slaves/’ in Secondary DNS server.

ls /var/named/slaves/

Sample Output:

learnwithak.fwd