DNS (Domain Name System)

• Definition: DNS, or Domain Name System, is a hierarchical and decentralized naming system for computers, services, or any resource connected to the Internet or a private network.
• Function: It translates human-readable domain names (like www.example.com) into IP addresses (like 192.0.2.1), which are required for locating and identifying computer services and devices.
• Components:
  • Domain Names: Structured in levels (e.g., .com, example.com, www.example.com).
  • DNS Records: Various types of records (A, AAAA, CNAME, MX, etc.) that store the mappings between domain names and IP addresses or other information.
  • DNS Servers:
    • Recursive Resolvers: Handle incoming requests from clients.
    • Root Name Servers: The starting point for DNS resolution.
    • TLD (Top-Level Domain) Servers: Manage the last part of the domain name (like .com, .org).
    • Authoritative Name Servers: Provide the actual IP address of the queried domain.
• Importance:
  • Usability: Facilitates web browsing by allowing users to access websites using easy-to-remember names.
  • Email Delivery: Helps route emails by translating domain names in email addresses to IP addresses.
  • Load Distribution: DNS can aid in distributing the load among multiple servers through techniques like round-robin DNS.
• Security Considerations: Vulnerable to attacks such as DNS spoofing or cache poisoning. Mechanisms like DNSSEC (Domain Name System Security Extensions) are implemented to mitigate such risks.

Connections :

• DNS serves as a crucial infrastructure underpinning the entire internet ecosystem, connecting web addressing (URLs) to machine addressing (IP addresses).
• The relationship between domain names and IP addresses highlights the need for effective and secure directory services in the networking domain.

• DNS Query Initiation:
  • User inputs a URL in a web browser (e.g., www.example.com).
  • The browser checks the local cache for the IP address associated with the domain.
• Local Cache Check:
  • If found, the IP address is used to establish a connection.
  • If not found, the query proceeds to the next step.
• DNS Resolver:
  • The query is sent to a DNS resolver (typically provided by the user's ISP).
  • The resolver checks its own cache for the requested domain.
• Root Name Servers:
  • If there’s no cached result, the resolver queries a root name server.
  • The root server responds with a referral to the appropriate top-level domain (TLD) server (e.g., .com, .org).
• TLD Name Servers:
  • The resolver queries the TLD name server for the domain.
  • The TLD server responds with a referral to the authoritative name server for the domain.
• Authoritative Name Servers:
  • The resolver queries the authoritative name server.
  • The authoritative server provides the final answer, returning the IP address for the requested domain.
• Response to User:
  • The resolver caches the IP address for future queries and sends the IP address back to the user’s browser.
  • The browser uses this IP address to establish a connection to the web server.
• Connection Establishment:
  • The browser initiates a TCP connection to the server using the retrieved IP address.
  • It then sends an HTTP request to access the website content.

• https://www.youtube.com/watch?v=27r4Bzuj5NQ&list=PLCRMIe5FDPsd0gVs500xeOewfySTsmEjf&index=2&ab_channel=ByteByteGo