DNS - DOMAIN NAME SYSTEM

Converts a hostname to an ip address and an ip address to a hostname. DNS is an embedded part of networks and systems. You can set up your own DNS server to have your own domain name and hostname resolution.

Fully-Qualified Domain Name FQDN a domanin name is witha top level provider .com

www.jimi421.com domain name is jimi421 top level domain is .com if you have ftp. blog. .jimi ect will create the fully qualified domain. there are 5 layers.

5 evels

root.

top level domain .com .net

second level domain jimi421.com

sub domain blog.jimi421.com

host rasberri-pi.home.jimi421.com

url has the full with the HTTPs://

Host file - a text fiel that servs as the first point of contact when a device wants to communicat with another device on the internet. hosts will check here first.

A i p v 4

AAAA - ip v 6

cname - points to another domain

mx - mail exchange record.

start of authortiy sores important info like zone transfer, which uses TCP.

reverse DNS lookup.

internal DNS is popular with cloud computing.

DNS uses recursive lookup, keeps workig up to the root to ask.

DNS Security - if you cna change the ip address in the DNS records hten you can cpaute the traffic and keep the login data, and redirect to the correct place.

DNS Serucity excentions - provides a digital tamper proof seal for DNS

DNS ofver HDDPs DoH - used to sedn DNS through the HTTPS protocol .

DNS over TLS (

jplaces DNS throuh a TLS tunnel.

Domain Name System (DNS) — Exam Notes

Purpose

Converts hostnames ⇄ IP addresses
Embedded in all networks and systems
Uses port 53
- UDP for queries (small messages)
- TCP for zone transfers/large messages

DNS Hierarchy (5 Levels)

Root – “.” (the invisible dot at the end of all FQDNs)
Top-Level Domain (TLD) – .com, .net, .org, .edu, country codes (.uk, .jp)
Second-Level Domain – e.g., jimi421.com
Subdomain – e.g., blog.jimi421.com
Host – e.g., raspberry-pi.home.jimi421.com

FQDN (Fully Qualified Domain Name) = Host + Domain + TLD (e.g., www.jimi421.com)

Records

A – maps hostname → IPV4
AAAA – maps hostname → IPV6
CNAME – alias; points one name to another
MX – mail exchanger (email delivery)
PTR – reverse lookup (IP → hostname)
SOA – Start of Authority; holds zone info (admin contact, refresh time, etc.)
NS – identifies authoritative name servers
TXT – human/machine-readable text (used for SPF, DKIM, domain verification)

Other Key Concepts

Hosts file – local text file, checked before DNS.
Recursive Lookup – DNS server queries other servers until answer found.
Iterative Lookup – DNS server gives referral to another server.
Zone Transfer – copy of DNS database (TCP).
Internal vs External DNS – internal for private networks/cloud, external for internet.

Security

DNS Poisoning / Spoofing – attacker changes DNS records to redirect traffic.
DNSSEC – cryptographic signatures; verifies authenticity (not encrypted, just signed).
DNS over HTTPS (DoH) – encrypts DNS in HTTPS traffic.
DNS over TLS (DoT) – encrypts DNS in a TLS tunnel.

Exam Tips

Port 53 = DNS
Zone transfers = TCP
Queries = UDP (unless too large)
DNSSEC = authenticity, not encryption
DoH/DoT = encrypt queries for privacy

✅ Common Question:

“Which record type is used for reverse lookups?” → PTR

“Which protocol does DNS use for zone transfers?” → TCP

“Which protocol does DNS use for queries?” → UDP (port 53)

Flashcard Trick: A → Address (IPV4), AAAA → IPV6 (4 A’s = 4x bigger), CNAME → Canonical Name, MX → Mail Exchange, PTR → Pointer (reverse).