Configuring DNS Server

DNS

• DNS(Domain Name System) is a hierarchical system used to translate human-readable domain names (e.g., example.com) into their respective machine-readable IP addresses (e.g., 192.0.2.1).
• In other words, a DNS Server resolves domain names into IP addresses and vice versa.

Structure/Components of DNS

• DNS consists of several components:-

  • Zones and Domains:

    • A zone is an administrative segment of the DNS namespace.
    • A domain is a node in the DNS tree (e.g., example.com).

  • DNS Records: These include

    • A (Address): It maps a domain to an IPv4 address format.
    • AAAA (Address): It maps a domain to an IPv6 address format.
    • CNAME (Canonical Name): This is the alias name for another domain.
    • MX (Mail Exchange): It specifies mail servers for a domain.
    • NS (Name Server): It indicates authoritative name servers for a domain.
    • PTR (Pointer): It maps an IP address to a domain (reverse DNS).
    • SOA (Start of Authority): It defines zone properties and the primary server.

Types of DNS Servers

• Authoritative DNS: This DNS stores and serves the DNS records for a domain.
• Recursive DNS: This DNS resolves domain queries by iteratively contacting authoritative servers.
• Caching DNS: This DNS temporarily stores query results to improve performance.

Configuring BIND (Berkeley Internet Name Domain)

• BIND is one of the most commonly used DNS server software.
• Here, BIND is applied for a domain such as ‘example.com’.

Installation

• • The BIND is installed using the package manager for the used Linux distribution. For example –
    • Debian/Ubuntu Linux :
      sudo apt update

      sudo apt install bind9 bind9utils bind9-doc
    • RHEL/CentOS Linux :
      sudo yum install bind bind-utils

Configuration Files

• • Primary Configuration File: /etc/bind/named.conf (Debian/Ubuntu) or /etc/named.conf (RHEL/CentOS).
  • Zone Files: Located in /var/named/ (RHEL/CentOS) or /etc/bind/ (Debian/Ubuntu).
  • Log Files: Usually found in /var/log/.

Basic Setup

• • To Edit the Main Configuration File:

• • • To add zones in the main Configuration file(named.conf):

• • To Create Zone Files:

• • • To Create the directory for zone files:

• • Example Details of Zone File (db.example.com):

• • Restart and Enable BIND:

• • Test Configuration:

    • The command named-checkconf is used to validate the configuration file and named-checkzone to verify the zone file:

      sudo named-checkconf

      sudo named-checkzone example.com /etc/bind/zones/db.example.com

Configuring a Caching DNS Server

• A caching DNS server improves performance by storing previously queried results locally in their cache, reducing DNS lookup times.

Steps to Configure a Caching DNS Server:

• • Step1 : Install BIND: 

• • • The BIND is installed using the package manager for the used Linux distribution. For example –
      • Debian/Ubuntu Linux :

• • • • RHEL/CentOS Linux :

• • Step2 : Modify the Configuration:

    • Edit the main configuration file:
      sudo nano /etc/bind/named.conf.options  # Debian/Ubuntu

      sudo nano /etc/named.conf               # RHEL/CentOS
    • Configure forwarding and enable recursion:

• • Step3 : Restart the DNS Service:

• • Step4 : Test the Caching Server:

    • The dig  command is used to query a domain and verify the response:
      dig example.com @127.0.0.1

Thus, the above setup provides a solid foundation for operating an authoritative or caching DNS server using BIND.

Summary of Commands Used in Configuring DNS