Understanding DNS: Domain Name System Explained

Understanding DNS (Domain Name System)

DNS (Domain Name System) is a protocol that manages and maintains a distributed database of IP addresses and domain names.

Uses of DNS

• Resolution: Converts domain names to IP addresses using a host.
• Inverse Resolution: Converts IP addresses to hostnames.
• Mail Routing: Determines the mail server for a given domain.

Domain Name Space

The domain name space is a distributed database stored across multiple machines. It stores the correspondence between domain names and IP addresses in a hierarchical structure.

TLDs (Top Level Domains)

Top Level Domains are the first level of the DNS organization, forming an inverted tree structure. They store the descendants of the root DNS domain. Examples include generic TLDs (.com, .net, .org) and geographical TLDs (.es, .fr, .it). Each DNS is a branch of this tree.

ICANN

ICANN (Internet Corporation for Assigned Names and Numbers) is the body responsible for managing root and TLD domains.

FQDN (Fully Qualified Domain Name)

An FQDN is the complete domain name for a specific host, including all parent domains separated by periods (e.g., www.example.com).

Domain Delegation

Domain delegation is a mechanism that decentralizes the administration of the DNS database by using subdomains. Control over these subdomains is delegated to another authority.

Domain

A domain is the set of a subtree and each of its lower nodes.

Area (Zone)

An area (or zone) is a set of nodes that are stored in a file to identify the domain database and handle requests.

Authoritative Name Server

An authoritative name server stores resource records for specific areas of the namespace and has authority over them. These servers can be primary or secondary.

Zone Transfer

Zone transfer is the mechanism by which a secondary server obtains zone information from a primary server.

DNS Database Protocol

The DNS database typically uses text file formats. There are two main types:

1. Zone file: For name resolution.
2. Reverse zone file: For reverse resolution (IP to name).

DNS servers query these files to resolve names, using resource records that contain domain information.

Format of DNS Records

The general format of a DNS record is: owner "Time To Live" class type rdata // value

Reply with Authority

When a server responds to a query, it can reply with authority (certain answer) or without authority (possible answer, but not definitive).

Search Server

• Recursive Search: If the server does not have the requested information, it queries the name server that contains the information.
• Iterative Search: The server returns the best answer it has. If it doesn't have the requested information, it provides the IP address of a name server that might have the answer.

SOA (Start of Authority)

The SOA record identifies the authoritative name server for a zone and its configuration parameters.