Introduction to DNS

• DNS: A decentralized system that translates domain names to IP addresses. Maps human-friendly domain names (e.g., google.com) to their corresponding IP addresses.
• Purpose: Ensures users do not need to memorize IP addresses. Allows users to access websites using domain names instead of IP addresses.
• Analogy: Similar to a phone book or contacts list where names map to phone numbers.
• Example: When accessing a website (e.g., google.com):
  • DNS translates domain names into IP addresses.
  • When a user types a domain name into their browser, the DNS system retrieves the corresponding IP address and sends it back to the client.
  • This allows the user's request to be directed to the appropriate server.
  • The server at the IP address responds, and the webpage is displayed.
  • Clients can access a website by entering either its domain name or its corresponding IP address in the browser.
    • Using a shell command (nslookup google.com) to get the IP address of a domain.
    • Demonstration of accessing Google by its IP address(142.251.211.238) directly, showing it leads to the same website as typing the domain name

Contributors to DNS Operations: ISPs, ICANN, and Registrars

• Internet Service Provider (ISP): Facilitates interaction with DNS servers.

• ICANN (Internet Corporation for Assigned Names and Numbers): Manages all domain names globally.

  • Ensures uniqueness of domain names.
  • Works with domain registrars to sell domains.

• Domain Registrars: Accredited resellers of domain names (e.g., Google Domains, Namecheap, GoDaddy).

  Steps Involved in Accessing Neetcode

  1. User Input:
     • The user enters neetcode.io into their browser.
  2. DNS Query Initiation:
     • The browser initiates a DNS query to resolve the domain name to an IP address.
     1. ISP Involvement:
        • The query is first sent to the user's Internet Service Provider (ISP).
        • The ISP checks its local DNS cache. If the IP address of neetcode.io is not found, it proceeds with further queries.
     2. DNS Server Query:
        • The ISP's DNS server queries the .io TLD DNS server, managed by the organization designated by ICANN for the .io domain.
        • read more about TLD DNS
     3. Domain Registrar's Role:
        • The .io TLD DNS server provides the address of the DNS server managed by the accredited registrar for neetcode.io (e.g., Google Domains, Namecheap, GoDaddy).
        • The registrar’s DNS server, which holds the authoritative DNS records for neetcode.io, returns the IP address.
  3. Response and Caching:
     • The ISP's DNS server receives the IP address, caches it for future queries, and sends it back to the client's browser.
  4. Establishing Connection:
     • The browser uses the IP address to establish a connection with Neetcode's server.
  5. Content Delivery:
     • Neetcode's server receives the request and sends the requested webpage back to the client.
  6. Page Display:
     • The browser displays the Neetcode webpage to the user.

Static and Dynamic IP Addresses

• Static IP Addresses: Rarely change, making DNS resolution straightforward.
• Dynamic DNS: Allows IP addresses to change but is less common

Caching

• Client-side Caching

When your device accesses a website, its DNS resolver saves the result. If you visit the same site again, the device uses the cached IP address, reducing query time and speeding up access.

• ISP Caching

ISPs cache DNS queries on their servers. If a query matches a cached entry, the ISP returns the IP address from its cache, cutting down on resolution time and reducing queries to upstream DNS servers.

URL Components

Breakdown of a URL: protocol, subdomain, domain name (primary domain), top-level domain (TLD), path, and parameters.