An Overview of DNS - N10-008 CompTIA Network+ : 1.6

Summary

This video explains the Domain Name System (DNS), a crucial protocol that translates human-readable domain names into IP addresses used by computers. It details how DNS functions as a distributed hierarchy, with root server clusters and top-level domains (TLDs) like .com, .org, and country-specific codes. The script explores recursive and iterative DNS queries, authority in DNS responses, time-to-live (TTL) values, and reverse DNS lookups. It also highlights DNS caching, potential issues with TTL, and the use of third-party DNS services like Google and Cloudflare for improved network performance.

Takeaways

• 😀 DNS (Domain Name System) translates human-readable domain names into IP addresses.
• 😀 Every time you visit a website, like www.professormesser.com, DNS is responsible for converting it into an IP address.
• 😀 DNS operates as a hierarchical system with different levels, including root servers, TLDs, and subdomains.
• 😀 There are 13 root DNS server clusters, with over 1,000 servers providing redundancy globally.
• 😀 Top-Level Domains (TLDs) can be generic (e.g., .com, .org) or country-specific (e.g., .US, .CA, .UK).
• 😀 The DNS hierarchy allows for the creation of Fully Qualified Domain Names (FQDNs) that not only specify devices but also their location within a network.
• 😀 Internal DNS servers are often used within organizations for local device resolution, and they may be managed on services like Windows Server or Linux.
• 😀 External DNS services, like Google DNS or Quad9, are commonly used to manage DNS queries for internet services.
• 😀 A recursive query allows a DNS server to resolve a domain name by querying multiple servers on behalf of the user.
• 😀 An iterative query requires the user’s device to resolve the DNS query by querying multiple servers directly.
• 😀 DNS query results come with a Time to Live (TTL) value, which determines how long the cached information stays valid before needing to be refreshed.

Q & A

What is the primary purpose of DNS?

The primary purpose of DNS (Domain Name System) is to translate human-readable domain names (like www.professormesser.com) into IP addresses that computers can use to communicate with each other.

How does DNS function in terms of hierarchy?

DNS is organized hierarchically, allowing for an easy structure of domain names. At the top are root servers, followed by TLD (Top Level Domain) servers like .com, .org, etc., and further subdivisions under each domain, such as subdomains like www or mail.

What are root servers in DNS?

Root servers are the topmost DNS servers in the hierarchy, responsible for directing DNS queries to the appropriate TLD servers. There are 13 primary root server clusters, with over 1,000 servers providing redundancy across the internet.

What is a fully qualified domain name (FQDN)?

A fully qualified domain name (FQDN) is the complete domain name for a specific computer or host, including the top-level domain, domain, and subdomains, such as www.professormesser.com.

What is the difference between a recursive and an iterative DNS query?

In a recursive DNS query, a local DNS server makes multiple requests on behalf of the client to resolve the IP address. In an iterative query, the client makes all the DNS requests directly to the servers, without relying on a central cache.

What role does caching play in DNS queries?

DNS servers cache query results to speed up future lookups. Cached results have a 'Time to Live' (TTL) value that determines how long they remain in the cache. Once the TTL expires, the cache is refreshed with a new query.

What is the Time to Live (TTL) in DNS?

Time to Live (TTL) is the amount of time that a DNS record is stored in a cache before it must be refreshed. A TTL value of 300 seconds means the record will be cached for 5 minutes.

What is the purpose of reverse DNS queries?

A reverse DNS query allows you to find the domain name associated with a specific IP address. This is the opposite of a forward lookup, which resolves a domain name to an IP address.

Why would DNS queries return a non-authoritative answer?

A non-authoritative answer is returned when the DNS information comes from the cache of the DNS server, rather than directly from the authoritative source. This may occur if the information is cached from a previous query.

What is the difference between internal and external DNS servers?

Internal DNS servers are typically used within an organization's network and managed by internal IT teams. External DNS servers are provided by third-party services like Google DNS or Quad9, and they resolve DNS queries for external websites.