The DNS resolution process involves translating human-readable domain names (like www.example.com
) into IP addresses that computers use for communication. It's a hierarchical process that requires cooperation between various DNS servers to provide accurate and efficient resolution.
Here's a detailed breakdown of the DNS resolution process:Local DNS Cache
DNS Client Query
- When a device (such as a computer or smartphone) wants to access a website, it checks its local DNS cache first. This cache stores recently resolved domain names and their corresponding IP addresses. If the desired domain name is found in the cache, the IP address can be retrieved directly, skipping the rest of the resolution process.
Iterative Query to Root DNS Servers
- If the domain name is not found in the local DNS cache, the device's DNS client sends a DNS query to a DNS resolver. The resolver is either provided by the Internet Service Provider (ISP) or a public DNS service like Google DNS or Cloudflare DNS.
Root DNS Server Response
- The DNS resolver starts the iterative query process by sending a query to one of the root DNS servers. The query contains the full domain name (e.g., www.example.com) and asks for the authoritative DNS server responsible for the top-level domain (TLD), in this case, the ".com" TLD.
Iterative Query to TLD DNS Server
- The root DNS server receives the query and responds with a referral to the TLD's authoritative DNS server. The referral includes the IP address of the TLD's authoritative server.
TLD DNS Server Response
- The DNS resolver sends another query, this time to the TLD's authoritative DNS server. The query asks for the authoritative DNS server responsible for the second-level domain, "example.com."
Authoritative DNS Server Query
- The TLD DNS server responds with another referral, providing the IP address of the authoritative DNS server for the second-level domain, "example.com."
Authoritative DNS Server Response
- The DNS resolver sends a final query to the authoritative DNS server for the specific domain, "example.com." This query asks for the IP address associated with the domain name "www.example.com."
Cache Update and Response
- The authoritative DNS server for "example.com" responds with the requested IP address for "www.example.com." This response is sent back through the DNS resolver to the original DNS client.
- The DNS resolver caches the received IP address along with the associated time-to-live (TTL) value. It also sends the IP address back to the DNS client, allowing the client to initiate a connection to the desired website's server.
- With the resolved IP address, the DNS client establishes a connection to the website's server using the IP address. This initiates the process of retrieving the website's content and displaying it in the user's web browser.
Throughout the DNS resolution process, caching at various stages helps optimize future queries by reducing the need to perform the complete resolution process for frequently accessed domain names. This hierarchical process ensures efficient and accurate translation of domain names to IP addresses, enabling seamless communication over the internet.