Master DNS Basics and Hands‑On BIND Configuration on CentOS

DNS Overview

DNS (Domain Name System) is a distributed database that maps domain names to IP addresses, replacing the hosts file with a hierarchical, inverted‑tree structure. The top level consists of 13 root servers managed by ICANN, followed by top‑level domain (TLD) servers, second‑level domains, and so on.

Resolution Types

Forward resolution converts FQDN to IP; reverse resolution converts IP to FQDN. Wildcard resolution can direct misspelled names to a specific address. Example:

$GENERATE 1-254 HOST$   A   1.2.3.$

Query Types

Recursive query: the client sends a single request and the DNS server resolves the entire chain. Iterative query: DNS servers refer the client to the next server in the hierarchy.

Zones and Resource Records

A zone is a portion of the DNS database; each zone contains resource records (RR) such as A, AAAA, PTR, SOA, NS, CNAME, MX. SOA (Start of Authority) is the first record in a zone and defines the zone’s authority.

Master‑Slave DNS

DNS operates on port 53 (UDP for queries, TCP for zone transfers). A primary (master) server holds the authoritative data; secondary (slave) servers obtain copies via push or pull mechanisms.

Setting Up BIND on CentOS

Install BIND: yum -y install bind. Disable the firewall: iptables -F and chkconfig iptables off (or disable firewalld on CentOS 7). Start the named service: service named start (or systemctl enable named and systemctl start named).

Configuration Files

/etc/named.conf

– main configuration file. /etc/named.rfc1912.zones – zone definitions. /var/named/ – directory for zone files.

Example zone definition for liansir99.com in /etc/named.rfc1912.zones:

zone "liansir99.com" IN {
    type master;
    file "liansir99.com.zone";
};

Corresponding zone file liansir99.com.zone:

$TTL 86400
@   IN  SOA ns1.liansir99.com. admin.liansir99.com. (
        2016100401 ; serial
        1H         ; refresh
        5M         ; retry
        7D         ; expire
        1D )       ; minimum
@   NS  ns1.liansir99.com.
@   MX  10 mail.liansir99.com.
ns1 A   10.1.1.1
slave A 10.1.1.4
www A   10.1.1.2
www A   10.1.1.3
mail A  10.1.1.5
ftp A   10.1.1.4
web CNAME ftp

Set proper ownership and permissions, then restart BIND:

chown named.named liansir99.com.zone
chmod 640 liansir99.com.zone
service named restart

Validate the configuration with named-checkconf and named-checkzone. Test using dig queries and verify that port 53 is reachable (UDP by default). The following images illustrate command output and configuration screenshots.