Set up a private master/slave DNS using BIND

One of the very basic need of any startup is setting up a LAN in the workspace and configuring the Internet most used service: DNS. Relying on a public DNS may give you full functionality towards WAN connectivity, but when you need to address some hosts inside your LAN it can be handy to use names instead of IPs (especially with IPv6).

Here’s a straight forward guide to get you started with your private DNS in a few minutes.

OS filesystem’s path and package management utility may vary with the flavour of your distro, here I use CentOS.


Requirements

  • a router with DHCP ad WAN connectivity already setup

  • 2 CentOS 6.x servers (physical or virtual with due availability concerns), enable to network with each others

  • a desktop PC


Some general info

I use this data as example, change them to your needs


**Configuring the primary DNS server **

On server centos1

[root@centos1 ~]# yum update && yum -y install bind bind-libs bind-utils

The BIND daemon is now installed; the base dir for the service is /var/named and the configuration file is /etc/named.conf ; modify the configuration file with your favourite editor

[root@centos1 ~]# vim /etc/named.conf

In the options section adjust the settings to your LAN configurations, changing the example values

options {
       listen-on port 53 { 10.20.30.40 };             # inet address of centos1
       listen-on-v6 port 53 { ::1; };                 # comment this out to use IPv4 only
       directory "/var/named";
       recursion yes;
       allow-recursion { 10.20.30.0/24; };            # recursion only in LAN, change this with your subnet
       allow-transfer { localhost; 10.20.30.50; };    # enable zone transfers only to secondary DNS sever
       forwarders {
                  208.67.222.222;
                  208.67.220.220;
       };                                             # OpenDNS used here, Google 8.8.8.8, 8.8.4.4 can be used
       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 { 10.20.30.0/24; };                # accept queries only from LAN, change this with your subnet
};

Now comment the include lines following the options section and comment out all the rest. The end of the file should be (modify the domain)

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

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

zone "startup.me" IN {
      type master;
      file "/var/named/startup.me.zone";
      allow-update { none; };
};

The latter lines create the definition of the domain and specify that DNS records should be looked up in the /var/named/startup.me.zone file which we are about to write. If you’re unfamiliar with DNS records and basic concepts, have a look at this. Now create and edit a new file

[root@centos1 ~]# vim /var/named/startup.me.zone

Insert this

$TTL 8H
@      IN      SOA      centos1.startup.me. root.startup.me. (
               1        ; serial
               1D       ; refresh
               1H       ; retry
               1W       ; expire
               1H )     ; minimum TTL
; Name servers
        IN      NS      centos1.startup.me.
        IN      NS      centos2.startup.me.
; Resolvers
@       IN      A       10.50.30.10  ; default IP for your domain root startup.me
centos1 IN      A       10.20.30.40  ; the primary DNS server centos1
centos2 IN      A       10.20.30.50  ; the secondary DNS server centos2
www     IN      A       10.20.30.20  ; a web server in your LAN
ftp     IN      A       10.20.30.30  ; an FTP server in your LAN
git     IN      A       10.20.30.5   ; a GIT server in your LAN

Be careful when copying the above snippet into the config file: indentation must be respected!

You have configured the primary DNS with some DNS A records; the provided settings are not for a heavy load DNS server, nor they should be used in networks wih frequent IP address change: the time-to-live settings are high, therefore any IP mapping change should be followed by a clients’ resolver cache flush, which may be inconvenient for most users.

Now it’s time to enable the service; verify files permission

[root@centos1 ~]# chown named /var/named/startup.me.zone

and start the service

[root@centos1 ~]# service named start

If you want to have the service enabled at boot

[root@centos1 ~]# chkconfig named on && chkconfig save

To test your primary DNS server you should first be sure to use it; check the resolver settings

[root@centos1 ~]# vim /etc/resolv.conf

it should contain only one line

nameserver 10.20.30.40

Verify the DNS is working with

[root@centos1 ~]# dig www.startup.me

if the output contains “AUTHORITY SECTION” you’re done.


**Configuring the secondary DNS server **

On server centos2 install BIND as you did for centos1.

[root@centos2 ~]# yum update && yum -y install bind bind-libs bind-utils

Secure-CoPy the configuration files from centos1 to centos2

[root@centos2 ~]# scp centos1.startup.me:/etc/named.conf /etc/named.conf

[root@centos2 ~]# scp centos1.startup.me:/var/named/startup.me.zone /var/named/startup.me.zone

Edit the /etc/named.conf adjusting the IPv4 address of centos2 in the options section, change 10.20.30.40 with 10.20.30.50, and at the end of the file modify the zone settings to have a secondary (slave) DNS; as usual, change the IP with your actual primary DNS IP.

zone "startup.me" IN {
      type slave;
      masters { 10.20.30.40; }; 
      file "/var/named/startup.me.zone";
};

Start the BIND daemon on centos2 and enjoy!

[root@centos2 ~]# chown named /var/named/startup.me.zone

[root@centos2 ~]# service named start

There it is! You are ready to test it from your desktop.

In your router settings change the primary and secondary DNS servers for the DHCP server, renew all adresses and try browsing the domain with any software. So name, much fast, wow!

Note: having a script doing an rsync to your secondary DNS will ease the pain when the primary DNS server goes down.

Cheers 😀

BIND  CentOS  DNS  Linux