DNS Resolution Process

DNS resolution is the process of converting domain names into IP addresses. When you enter www.example.com into your browser, the computer finds the corresponding IP address through the following steps:

1. Browser Cache Query

• The browser first checks its own cache to see if it has saved the IP address for the domain.
• If a valid cache entry is found and it has not expired, the IP address is used directly.
• The cache duration is determined by the TTL (Time To Live) value in the DNS record.

2. System Cache Query

• If not found in the browser cache, the operating system cache is checked.
• Windows systems check the hosts file; Linux/Mac systems check /etc/hosts.
• The system DNS resolver cache is also checked (e.g., the DNS Client service in Windows).

3. Router Cache Query

• The request is sent to the local router, which may have cached DNS records.
• Many home routers have DNS caching functionality.

4. Local DNS Server Query

• If none of the above caches have the record, the request is sent to the local DNS server (usually provided by the ISP).
• Local DNS servers typically maintain a large cache database.
• The query process is recursive, meaning the local DNS server takes responsibility for completing the entire lookup.

5. Root Name Server Query

• If the local DNS server has no cache, it first queries a root name server.
• There are 13 groups of root name servers globally (with many more mirrored instances).
• Root servers do not directly resolve domain names but return the addresses of the authoritative servers for the corresponding top-level domain (e.g., .com).

6. Top-Level Domain (TLD) Server Query

• The local DNS server then queries the .com TLD server.
• The TLD server returns the address of the authoritative DNS server responsible for example.com.

7. Authoritative Name Server Query

• Finally, the local DNS server queries the authoritative DNS server for example.com.
• The authoritative server returns the exact IP address for www.example.com.

8. Cache and Return Result

• The local DNS server caches the result (according to the TTL value).
• It returns the IP address to the client.
• The client also caches this result for future use.

Optimization Features of the Entire Resolution Process:

• Caching mechanisms significantly reduce the number of actual queries.
• Iterative and recursive queries are used in combination.
• There are multiple types of DNS records (A, AAAA, CNAME, MX, etc.).
• Supports load balancing and failover capabilities.

This process ensures the efficiency and reliability of domain name resolution and is a vital component of modern internet infrastructure.