Understanding Absolute and Relative Domain Names in DNS
In the Domain Name System (DNS), domain names can be specified with or without a trailing dot, which can affect how DNS resolvers interpret and resolve the names. In this blog post, we’ll explore the differences between absolute and relative domain names and how they impact DNS resolution.
Absolute Domain Names:
When a domain name ends with a dot (e.g., “example.com.”), it is considered an absolute domain name. Absolute domain names instruct DNS resolvers to perform a lookup only for the exact domain specified, without appending any additional domain suffixes. Here’s how DNS resolution works for absolute domain names:
DNS Resolver Behavior: The DNS resolver interprets the domain name as an absolute reference and sends a query specifically for that exact domain to the DNS root servers.
DNS Root Servers: The root servers respond with information about the top-level domain (TLD) servers responsible for the specified TLD (e.g., “.com”).
TLD Servers: The resolver queries the TLD servers for information about the authoritative name servers responsible for the specified domain.
Authoritative Name Servers: Finally, the resolver queries the authoritative name servers for the specified domain to obtain the associated IP addresses.
Relative Domain Names:
In contrast, when a domain name does not end with a dot (e.g., “example.com”), it is considered a relative domain name. Relative domain names may prompt DNS resolvers to append search domains or suffixes to complete the resolution process. Here’s how DNS resolution works for relative domain names:
DNS Resolver Behavior: The DNS resolver attempts to resolve the domain name without any additional suffixes.
Search Domain Configuration: If the resolver is configured with search domains, it may append these domains to the specified domain name in a specific order.
Recursive Resolution: The resolver performs recursive DNS resolution for each modified domain name, querying the appropriate DNS servers to obtain the IP addresses associated with the domain’s records.
Conclusion:
Understanding the distinction between absolute and relative domain names is essential for DNS resolution. By specifying domain names appropriately, you can control how DNS resolvers interpret and resolve queries, ensuring accurate and efficient resolution of domain names.
