DNS resolution process

DNS Terminology

When we talk about DNS there are a lot of concepts that are always mentioned: TLD, FQDN, HOST, DOMAIN, SUBDOMAIN but what does that even mean? or how can this be easily understood?

Figure #1. Binary tree example
Figure #2. Filling our tree
Figure #3. Breaking down the tree
  • TLD (Top Level Domain): The first stop after the Root name server, this contains: com, org, net, UK, edu, etc. There are also different types, the generics (gTLD), country code (ccTLD), Sponsored (sTLD), and reserved TLD like .localhost or .example which are not permanently available.
  • domain name: Like in the yellow-pages in the old times, associate a human-readable name to an IP via DNS A records to IPv4 or AAAA records to IPv6
  • Subdomain: A domain that is a part of another domain, in this case, the domain name.

DNS resolution process

When you type google.com there is a lot of “magic” going behind scenes, but how does that magic work? The DNS runs on port 53 and helps us to resolve a HOST to IP address, based on some DNS Records, the A, and AAAA respectively, there are other DNS record types such as the image below, but the important thing here to know is that DNS works like the old yellow pages where you were able to find phone numbers (IP’s) based on someone’s name (domain name)

Figure#4 DNS Record Types
Figure#5. DNS Resolution process

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Sr. Security software engineer working in the DevSecOps area. CompTIA Sec+, C|EH

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Josué Carvajal

Sr. Security software engineer working in the DevSecOps area. CompTIA Sec+, C|EH