TryHackMe DNS Room Lecture Notes

Introduction to DNS

• Presenter: John
• Platform: TryHackMe
• Topic: Detailed exploration of DNS (Domain Name System)
• Purpose: Understand how DNS works and its role in accessing internet services

Task 1: What is DNS?

• DNS Definition: Domain Name System allows communication with internet devices without remembering complex IP addresses.
• IP Address: Unique address for internet communication, typically four sets of numbers (0-255), separated by periods (four octets).
• DNS Function: Converts human-friendly domain names (e.g., tryhackme.com) to IP addresses.

Task 2: Domain Hierarchy

TLD (Top Level Domains)

• Definition: Rightmost part of a domain (e.g., .com in tryhackme.com).
• Types:
  • gTLD (Generic): Indicates domain purpose (e.g., .com, .org, .edu).
  • ccTLD (Country Code): Indicates geographical location (e.g., .ca, .co.uk).
• New TLDs: Frequent introductions of new TLDs (e.g., .online, .biz).
• Action: Suggests exploring domain registration sites for more TLDs.

Second Level Domain

• Example: trihackme in tryhackme.com.
• Restrictions: Up to 63 characters, using A-Z, 0-9, and hyphens (no hyphens at start/end or consecutive hyphens).

Subdomains

• Example: admin in admin.tryhackme.com.
• Structure: Can have multiple subdomains (e.g., jupiter.servers.tryhackme.com).
• Restrictions: Similar to second level domains; no limit on the number of subdomains.
• Importance: Relevant in web hacking and cookie management.

Task 3: DNS Record Types

Common DNS Record Types

• A Record: Resolves domain to an IPv4 address.
• Pointer Record: Reverse lookup, finds domain associated with an IP.
• Quad A Record: Resolves domain to an IPv6 address.
• CNAME Record: Alias for domain names, resolves to another domain.
• MX Record: Directs email to mail servers for a domain.
• TXT Record: Stores arbitrary text, used for email verification and anti-spam measures.

Task 4: Making a DNS Request

DNS Request Process

1. Local Cache Check: Checks if domain address is cached locally on computer.
2. Recursive DNS Server: Provided by ISP, checks its cache and contacts root DNS servers if not found.
3. Root DNS Servers: Redirect to appropriate TLD server based on request.
4. TLD Servers: Directs to authoritative name server for domain.
5. Authoritative DNS Server: Stores DNS records and updates; sends records back to recursive server.

• TTL (Time to Live): Specifies how long DNS record should be cached locally.

Task 5: Practical DNS Queries

• CNAME Query: Determine canonical name for subdomains.
• TXT Record Query: Retrieve text records for domains.
• MX Record Priority: Find priority value for mail exchange records.
• A Record Query: Obtain IP address for domain records.

Conclusion

• Resources: TryHackMe Discord & Subreddit for further questions.
• Note: Always practice and explore further to solidify understanding of DNS and its applications.