Add 'Bind9 DNS Server'

Bind9-DNS-Server.md

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+### How to Install and Configure DNS Server (Bind 9) on Ubuntu / Debian
+
+DNS or Domain Name System, as we know is an internet service that is used to translate the user friendly domain into computer friendly IP addresses. Not only can we translate domain names to IP addresses, we can also perform reverse translation i.e. from IP addresses to domain name translations. In this tutorial, we are going to learn to setup a private DNS server by implementing BIND9 on Ubuntu/Debian system.
+
+BIND or BIND 9 is an open source implementation of DNS, available for almost all Linux distributions. BIND stands Berkeley Internet Name Domain & it allows us to publish DNS information on internet as well as allows us to resolve DNS queries for the users. BIND is by far the most used DNS software on Internet. In this tutorial i will be using followings:
+
+Bind Server IP (Ubuntu / Debian) = 192.168.0.40
+Domain Name = linuxtechi.local
+Private Network = 192.168.0.0/24
+So let’s start the tutorial with the installation on packages for BIND 9….
+
+### Installation of Bind 9 on Debian / Ubuntu System:
+We need to install ‘bind9 bind9utils bind9-doc dnsutils’ to install BIND 9 & related tools. Open your terminal & execute the following command:
+```
+linuxtechi@bind-server:~$ sudo apt-get install bind9 bind9utils bind9-doc dnsutils
+```
+
+### Configuration of bind 9 on Debian / Ubuntu System:
+Once all the packages have been installed, we will move into the configuration part. All configuration files for BIND are located in folder ‘/etc/bind’.
+
+One of the important configuration file for bind is “/etc/bind/named.conf.options“, from this file we can set the followings parameters:
+
+Allow Query to your dns from your private network (As the name suggests only the systems from your private network can query dns sever for name to ip translation and vice-versa)
+Allow recursive query
+Specify the DNS port ( 53)
+Forwarders (DNS query will be forwarded to the forwarders when your local DNS server is unable to resolve query)
+As per my private network settings, I have specified the following parameters:
+
+```
+linuxtechi@bind-server:~$ sudo vi /etc/bind/named.conf.options
+options {
+        directory "/var/cache/bind";
+        auth-nxdomain no;    # conform to RFC1035
+     // listen-on-v6 { any; };
+        listen-on port 53 { localhost; 192.168.0.0/24; };
+        allow-query { localhost; 192.168.0.0/24; };
+        forwarders { 8.8.8.8; };
+        recursion yes;
+        };
+```
+
+Next Important Configuration file is “/etc/bind/named.conf.local“, in this file we will define the zone files for our domain, edit the file add the following entries:
+```
+linuxtechi@bind-server:~$ cd /etc/bind
+linuxtechi@bind-server:~$ sudo vi named.conf.local
+zone    "linuxtechi.local"   {
+        type master;
+        file    "/etc/bind/forward.linuxtechi.local";
+ };
+
+zone   "0.168.192.in-addr.arpa"        {
+       type master;
+       file    "/etc/bind/reverse.linuxtechi.local";
+ };
+```
+
+Save the file & exit. Here we have mentioned locations for our forward lookup zone file & reverse lookup zone files. Next we will create the mentioned forward & reverse zone files.
+
+Firstly create the forward lookup zone file, Sample zone files (db.local) are already there in ‘**/etc/bind folder**‘, we can use and copy sample zone file:
+```
+linuxtechi@bind-server:/etc/bind$ sudo cp db.local forward.linuxtechi.local
+linuxtechi@bind-server:/etc/bind$ sudo vi forward.linuxtechi.local
+$TTL    604800
+
+@       IN      SOA     primary.linuxtechi.local. root.primary.linuxtechi.local. (
+                              6         ; Serial
+                         604820         ; Refresh
+                          86600         ; Retry
+                        2419600         ; Expire
+                         604600 )       ; Negative Cache TTL
+
+;Name Server Information
+@       IN      NS      primary.linuxtechi.local.
+
+;IP address of Your Domain Name Server(DNS)
+primary IN       A      192.168.0.40
+
+;Mail Server MX (Mail exchanger) Record
+linuxtechi.local. IN  MX  10  mail.linuxtechi.local.
+
+;A Record for Host names
+www     IN       A       192.168.0.50
+mail    IN       A       192.168.0.60
+
+;CNAME Record
+ftp     IN      CNAME    www.linuxtechi.local.
+```
+
+Your forward lookup file should look like something below:
+```
+linuxtechi@bind-server:/etc/bind$ sudo cp db.127 reverse.linuxtechi.local
+linuxtechi@bind-server:~$ sudo vi /etc/bind/reverse.linuxtechi.local
+$TTL    604800
+@       IN      SOA     linuxtechi.local. root.linuxtechi.local. (
+                             21         ; Serial
+                         604820         ; Refresh
+                          864500        ; Retry
+                        2419270         ; Expire
+                         604880 )       ; Negative Cache TTL
+
+;Your Name Server Info
+@       IN      NS      primary.linuxtechi.local.
+primary IN      A       192.168.0.40
+
+;Reverse Lookup for Your DNS Server
+40      IN      PTR     primary.linuxtechi.local.
+
+;PTR Record IP address to HostName
+50      IN      PTR     www.linuxtechi.local.
+60      IN      PTR     mail.linuxtechi.local.
+```
+
+Save file & exit. Now all we have to do is to restart the BIND service to implement the changes made.
+
+```
+linuxtechi@bind-server:~$ sudo systemctl restart bind9
+linuxtechi@bind-server:~$ sudo systemctl enable bind9
+```
+
+**Note**: In case OS firewall is running on your bind server then execute the below command to allow 53 port
+```
+linuxtechi@bind-server:~$ sudo ufw allow 53
+Rule added
+Rule added (v6)
+linuxtechi@bind-server:~$
+```
+
+### Validating Syntax of bind9 configuration and Zone files
+If you want to cross verify the syntax of your bind 9 configuration file (named.conf.local). Use the command “named-checkconf“, example is shown below:
+```