Routing And Switching Questions Long
DNS resolution is the process by which domain names are translated into IP addresses, allowing web browsing to occur. When a user enters a domain name into a web browser, such as www.example.com, the browser needs to know the IP address associated with that domain in order to establish a connection and retrieve the requested web page. The DNS resolution process involves several steps:
1. Local DNS Cache: The first step in DNS resolution is to check the local DNS cache on the user's device or the local network. This cache stores previously resolved domain names and their corresponding IP addresses. If the domain name is found in the cache and the stored IP address is still valid, the resolution process can be skipped, and the browser can directly connect to the IP address.
2. Recursive DNS Servers: If the domain name is not found in the local DNS cache, the next step is to contact a recursive DNS server. These servers are responsible for resolving domain names on behalf of clients. The recursive DNS server may have its own cache, which it checks first before proceeding further.
3. Root DNS Servers: If the recursive DNS server does not have the IP address for the requested domain name in its cache, it contacts a root DNS server. Root DNS servers are the highest level in the DNS hierarchy and maintain a database of IP addresses for top-level domains (TLDs) such as .com, .org, .net, etc. The recursive DNS server queries the appropriate root DNS server based on the TLD of the requested domain name.
4. TLD DNS Servers: The root DNS server responds to the recursive DNS server with the IP address of the TLD DNS server responsible for the requested domain name's TLD. The recursive DNS server then queries the TLD DNS server for the IP address of the authoritative DNS server for the specific domain.
5. Authoritative DNS Servers: The authoritative DNS server is responsible for storing the IP addresses associated with the domain names it manages. The recursive DNS server contacts the authoritative DNS server for the requested domain name and requests the IP address.
6. DNS Response: The authoritative DNS server responds to the recursive DNS server with the IP address of the requested domain name. The recursive DNS server caches this IP address for future use and sends it back to the user's device.
7. Web Browsing: With the IP address obtained from the DNS resolution process, the user's device can now establish a connection to the web server associated with the requested domain name. The web server then delivers the requested web page to the user's browser, enabling web browsing to occur.
Overall, the DNS resolution process involves multiple steps, starting from the local DNS cache and progressing through recursive DNS servers, root DNS servers, TLD DNS servers, and authoritative DNS servers. This process ensures that domain names are translated into their corresponding IP addresses, allowing users to access websites and browse the internet.