Answer:
The Domain Name System (DNS) is a fundamental component of the internet infrastructure that serves as a decentralized naming system for identifying and locating resources on the internet. Its primary purpose is to translate human-readable domain names into IP addresses, which are numerical identifiers used by computers to communicate with each other.
Step-by-step explanation:
A valid domain name consists of two or more parts separated by dots, also known as labels. Each label can contain up to 63 characters and can consist of letters (a-z), numbers (0-9), and hyphens (-). The total length of a domain name, including all labels and dots, cannot exceed 253 characters. Additionally, domain names are case-insensitive, meaning uppercase and lowercase letters are treated the same.
The structure of a valid domain name follows a hierarchical system, starting from the rightmost label and moving towards the left. The rightmost label represents the top-level domain (TLD), which can be generic (e.g., .com, .org) or country-specific (e.g., .us, .uk). The second-level domain (SLD) appears to the left of the TLD and represents the main identifier for a website or organization. Subdomains can be added to the left of the SLD, forming a hierarchical structure that allows for further categorization or organization of resources.
For example, in the domain name "www.example.com," "com" is the TLD, "example" is the SLD, and "www" is a subdomain. This structure helps in organizing websites and facilitating easy navigation on the internet.
The DNS operates through a distributed network of servers called DNS servers or resolvers. When a user enters a domain name in their web browser or any other application that requires internet connectivity, the DNS resolver initiates a series of queries to locate the corresponding IP address.
The DNS resolution process involves multiple steps:
1. Local Caching: The resolver first checks its local cache to see if it has previously resolved the domain name. If a match is found, the corresponding IP address is returned.
2. Recursive Query: If the domain name is not found in the local cache, the resolver sends a recursive query to one of the root DNS servers. These root servers maintain a database of authoritative DNS servers for each TLD.
3. TLD Resolution: The root DNS server responds to the resolver with a referral to the appropriate TLD DNS server based on the requested domain name's TLD. The resolver then sends another query to the TLD DNS server.
4. Authoritative Resolution: The TLD DNS server responds with a referral to the authoritative DNS server responsible for the requested domain name's SLD. The resolver sends a final query to this authoritative DNS server.
5. IP Address Retrieval: The authoritative DNS server provides the IP address associated with the requested domain name back to the resolver, which then caches this information for future use.
6. Response to User: Finally, the resolver returns the IP address to the user's application, allowing it to establish a connection with the desired resource on the internet.
The DNS system ensures that users can access websites and other internet resources using human-readable domain names instead of relying solely on numerical IP addresses. It simplifies internet navigation and enables efficient communication between computers across the globe.