DNS and Domain Name System

Introduction to DNS

• DNS (Domain Name System) is used to translate domain names into IP addresses for connecting to servers.
• Example: Translating www.professormesser.com to its associated IP address.
• DNS functions as a hierarchical database.

DNS Hierarchy and Structure

• DNS is not just a single server but consists of multiple server clusters.
• Root DNS servers consist of 13 clusters, managing top-level domains (TLDs) like .com, .org, .net, and country codes like .us, .ca.
• Fully Qualified Domain Name (FQDN): A structured naming system, e.g., www.professormesser.com.

Redundancy and DNS Configuration

• Redundant DNS servers are used for maintaining uptime and availability.
• Primary and secondary DNS servers:
  • Primary DNS server handles zone information and configurations directly.
  • Secondary DNS server receives read-only updates from the primary server.
• Systems typically have configurations for primary and secondary DNS.

Local Name Resolution

• Local name resolution allows DNS resolution on a local machine without querying a DNS server.
• Utilizes a "hosts" file to map IP addresses to domain names locally.
• Important for testing or correcting DNS information locally.

Forward and Reverse DNS Lookup

• Forward Lookup: Provides an IP address for a given domain name.
• Reverse Lookup: Provides domain name for a given IP address.
• Tools like dig and NSLookup are used for performing these lookups.

Authoritative vs Non-Authoritative DNS Servers

• Authoritative Server: The primary source for DNS zone information.
• Non-Authoritative Answers: Information from cached results, not directly from the authoritative server.
• Time to Live (TTL) determines how long DNS information is cached.

DNS Query Process and Recursive Queries

• DNS queries can be recursive, meaning local DNS servers query root servers and TLDs to resolve domain names.
• Process involves resolvers, local DNS servers, root servers, and authoritative servers.

Security Concerns and Solutions in DNS

• DNS traditionally lacks security, with unencrypted and unauthenticated responses.
• DNSSEC: Adds digital signatures to DNS responses for verification.
• DNS over TLS (DOT) and DNS over HTTPS (DOH): Encrypts DNS traffic, enhancing privacy and security.

Conclusion

• DNS is a crucial service for internet connectivity, requiring careful configuration and security measures.
• Emerging technologies like DNSSEC, DOT, and DOH are improving the security and reliability of DNS services.