TryHackMe: DNS in Detail — Learning Notes

These are my personal learning notes as I work through TryHackMe — honest notes, not an authoritative guide. Corrections welcome.

Overview

• Room: DNS in Detail — link
• Difficulty: Info / Easy
• What it teaches: What DNS actually is, how a domain name is structured, and the main types of DNS records that make websites and email work.

What DNS actually does

The simplest way I can put it: DNS is a translator. Computers find each other using numerical addresses (IP addresses), but humans are terrible at remembering numbers. DNS lets us type a human-friendly name — an “English” address — and quietly converts it into the numerical one the machines actually use. Every time you visit a site by name, a DNS lookup happened in the background to turn that name into an IP.

Anatomy of a domain name

A domain name isn’t one flat thing — it’s built in layers, read right to left:

• Subdomain — the leftmost part (e.g. the blog in blog.example.com). A site can have many.
• Second-level domain — the main registered name (the example in example.com).
• Top-level domain (TLD) — the ending (.com, .my, etc).

TLDs themselves split into two families:

• gTLD (generic) — categorised by purpose. For example .edu for educational sites and .gov for government.
• ccTLD (country-code) — tied to a country. For example .my for Malaysia.

DNS record types

A domain’s DNS records are the actual instructions that say “this name points here.” The ones the room covered:

Record	What it maps to	Plain-language example
A	An IPv4 address (xxx.xxx.xxx.xxx)	“This domain lives at this IPv4 address.”
AAAA	An IPv6 address (xx:xx:xx::xx:xx)	Same idea as A, but for the newer, longer IPv6 addresses.
CNAME	Another domain name	Points one name at another. E.g. shop.mywebsite.com is a CNAME to mycustomshop.shopify.com — so the shop subdomain “jumps to” Shopify.
MX	A mail server	Says where email for the domain should go. E.g. mywebsite.com’s mail is handled by an external mail server.
TXT	Free-form text	Holds arbitrary text records. I don’t fully understand yet why these matter — flagged for a revisit below.

The A/AAAA/CNAME/MX group clicked fairly quickly once I saw them side by side: A and AAAA are “where the site is,” CNAME is “actually, go look at this other name instead,” and MX is “where the email goes.” TXT is the odd one out that I haven’t got a handle on.

Lessons Learned

• New to me: The whole layered structure of a domain — subdomain, second-level, TLD — and that TLDs are categorised either by purpose (gTLD) or by country (ccTLD).
• What surprised me: .com was originally meant for commercial sites specifically. That meaning has completely eroded — now everyone wants a .com, even for a personal blog. The label outlived its original intent.
• What I found tough: Keeping the record types straight. Writing out what each one maps to (above) is what made them stick — A/AAAA to IP addresses, CNAME to another name, MX to a mail server.
• Revisit: TXT records. I genuinely don’t yet see why a free-text DNS record is useful — that’s the gap I want to close next.

References

• The room’s guided tasks on TryHackMe