Subdomain

[2] The full domain name may not exceed a total length of 253 ASCII characters in its textual representation.

Network Operations teams insist that it is inappropriate to use the term "subdomain" to refer to any mapping other than that provided by zone NS (name server) records and any server-destination other than that.

Hosting services typically provide DNS Servers to resolve subdomains within that master domain.

Automated tools like Amass[5] and Subfinder [6] leverage open-source intelligence and SSL certificate data[7] to quickly uncover subdomains.

Google Dorking, using the "site:" operator, allows for manual searches of indexed subdomains, while brute force techniques systematically query DNS servers with potential names.

Passive DNS reconnaissance through APIs from services like SecurityTrails & Subdomain Center[8] can reveal historical data without direct queries.

Combining these approaches will enhance your ability to effectively identify hidden or overlooked subdomains for security assessments or research purposes.

[12] Depending on application, a record inside a domain, or subdomain might refer to a hostname, or a service provided by a number of machines in a cluster.