Default Configuration
There are many different configuration types for DNS. Therefore, we will only discuss the most important ones to illustrate better the functional principle from an administrative point of view. All DNS servers work with three different types of configuration files:
local DNS configuration files
zone files
reverse name resolution files
The DNS server Bind9 is very often used on Linux-based distributions. Its local configuration file (named.conf) is roughly divided into two sections, firstly the options section for general settings and secondly the zone entries for the individual domains. The local configuration files are usually:
named.conf.localnamed.conf.optionsnamed.conf.log
It contains the associated RFC where we can customize the server to our needs and our domain structure with the individual zones for different domains. The configuration file named.conf is divided into several options that control the behavior of the name server. A distinction is made between global options and zone options.
Global options are general and affect all zones. A zone option only affects the zone to which it is assigned. Options not listed in named.conf have default values. If an option is both global and zone-specific, then the zone option takes precedence.
Local DNS Configuration
DNS
root@bind9:~# cat /etc/bind/named.conf.local
//
// Do any local configuration here
//
// Consider adding the 1918 zones here, if they are not used in your
// organization
//include "/etc/bind/zones.rfc1918";
zone "domain.com" {
type master;
file "/etc/bind/db.domain.com";
allow-update { key rndc-key; };
};In this file, we can define the different zones. These zones are divided into individual files, which in most cases are mainly intended for one domain only. Exceptions are ISP and public DNS servers. In addition, many different options extend or reduce the functionality. We can look these up on the documentation of Bind9.
A zone file is a text file that describes a DNS zone with the BIND file format. In other words it is a point of delegation in the DNS tree. The BIND file format is the industry-preferred zone file format and is now well established in DNS server software. A zone file describes a zone completely. There must be precisely one SOA record and at least one NS record. The SOA resource record is usually located at the beginning of a zone file. The main goal of these global rules is to improve the readability of zone files. A syntax error usually results in the entire zone file being considered unusable. The name server behaves similarly as if this zone did not exist. It responds to DNS queries with a SERVFAIL error message.
In short, here, all forward records are entered according to the BIND format. This allows the DNS server to identify which domain, hostname, and role the IP addresses belong to. In simple terms, this is the phone book where the DNS server looks up the addresses for the domains it is searching for.
Zone Files
DNS
For the IP address to be resolved from the Fully Qualified Domain Name (FQDN), the DNS server must have a reverse lookup file. In this file, the computer name (FQDN) is assigned to the last octet of an IP address, which corresponds to the respective host, using a PTR record. The PTR records are responsible for the reverse translation of IP addresses into names, as we have already seen in the above table.
Reverse Name Resolution Zone Files
DNS
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