Describe the process of Domain Name System (DNS) resolution.

The Domain Name System (DNS) resolution is the process of converting human-readable domain names into IP addresses, which are numerical identifiers used to locate and identify devices on a network. This process involves several steps:

1. User Input: The process begins when a user enters a domain name (e.g., www.example.com) into a web browser or any other application that requires network communication.

2. Local DNS Cache: The local DNS resolver on the user's device checks its cache to see if it already has the IP address corresponding to the domain name. If the information is present and not expired, the resolver can skip the remaining steps and directly provide the IP address.

3. Recursive Query: If the IP address is not found in the local cache, the resolver sends a recursive query to the DNS resolver of the user's Internet Service Provider (ISP). This resolver is responsible for handling DNS queries on behalf of its users.

4. Root DNS Servers: If the ISP resolver does not have the IP address in its cache, it contacts one of the 13 root DNS servers worldwide. These root servers maintain a database of the top-level domain (TLD) servers responsible for specific domain extensions (.com, .org, .net, etc.).

5. TLD DNS Servers: The root DNS server responds to the ISP resolver with the IP address of the TLD DNS server responsible for the requested domain extension. For example, if the domain is www.example.com, the TLD DNS server for the ".com" extension is contacted.

6. Authoritative DNS Servers: The TLD DNS server provides the IP address of the authoritative DNS server responsible for the specific domain name. The authoritative DNS server is typically managed by the organization that owns the domain name (e.g., example.com).

7. DNS Resolution: The ISP resolver sends a query to the authoritative DNS server, requesting the IP address for the given domain name. The authoritative DNS server responds with the IP address, which is then passed back to the user's device through the recursive query path.

8. Local DNS Cache Update: The resolver on the user's device stores the IP address in its local cache for future use, reducing the need for repeated DNS resolution for the same domain name.

9. Communication Establishment: With the IP address obtained, the user's device can establish a connection with the desired server associated with the domain name. This allows the user to access the website or service they intended to reach.

Overall, the DNS resolution process involves multiple layers of DNS servers, starting from the root servers and gradually narrowing down to the authoritative DNS server responsible for the specific domain name. This hierarchical structure allows for efficient and reliable resolution of domain names into IP addresses, enabling seamless communication over the internet.