Chapter 5 — Session 7: DNS Part 1

This session is about DNS basics + record types. Your Chapter 5 source specifically lists DNS port 53, FQDNs, and the high-yield records A, AAAA, CNAME, MX, NS, PTR, SOA, TXT, SRV, and CAA.

📋 Topics to Mark Off

• ⬜ DNS

• ⬜ FQDN

• ⬜ UDP 53

• ⬜ TCP 53

• ⬜ A record

• ⬜ AAAA record

• ⬜ CNAME

• ⬜ MX

• ⬜ NS

• ⬜ PTR

• ⬜ SOA

• ⬜ TXT

• ⬜ SRV

• ⬜ CAA

• ⬜ Forward lookup

• ⬜ Reverse lookup

📝 Notebook Notes — Quick Review

📖 DNS

DNS = Domain Name System

DNS translates human-friendly names into IP addresses.

google.com
    ↓
DNS
    ↓
IP address

Think:

DNS = Internet phone book 📖

Your source describes DNS as resolving human names to IP addresses.

🏷 FQDN

FQDN = Fully Qualified Domain Name

It contains:

Hostname + Domain Name

Example from your chapter:

www.lammle.com

Break it apart:

www        = hostname
lammle.com = domain

www.lammle.com
      ↓
     FQDN

🧠 Memory

FQDN = Full name of the device.

Like:

First name + last name

⭐ DNS Port 53 — EXAM GOLD

Normal DNS queries use:

UDP 53

DNS zone transfers/updates use:

TCP 53

🧠 Memory

DNS = 53

Then remember:

Normal query → UDP 53

Zone transfer → TCP 53

🅰️ A Record ⭐

An A record maps:

Hostname → IPv4 address

Example:

server.example.com
        ↓
192.168.1.50

Your source defines A as Name → IPv4.

🧠 Memory

A = Address = IPv4

🅰🅰🅰🅰 AAAA Record ⭐

An AAAA record maps:

Hostname → IPv6 address

Example:

server.example.com
        ↓
2001:db8::50

🧠 Memory

AAAA = IPv6 is the BIG address.

Four A's for the longer address.

🔗 CNAME

CNAME = Canonical Name

It creates an:

Alias

One hostname points to another hostname.

Example:

shop.example.com
        ↓
store.example.com

The chapter defines CNAME as an alias from one name to another.

🧠 Memory

CNAME = nickname.

Your legal name might be:

Robert

But everyone calls you:

Bob

CNAME works similarly.

📧 MX Record ⭐

MX = Mail Exchanger

MX tells DNS:

Which mail server handles email for the domain.

Example:

example.com
    ↓
MX
    ↓
mail.example.com

Your source also notes that the lowest MX priority number is tried first.

🧠 Memory

MX = Mail eXchanger 📧

🧭 NS Record

NS = Name Server

It identifies:

The authoritative DNS server for a domain.

Think:

example.com
    ↓
"Who knows the official DNS records?"
    ↓
NS
    ↓
DNS Server

🧠 Memory

NS = Name Server

Simple one.

🔄 PTR Record ⭐⭐⭐ EXAM GOLD

PTR is used for:

Reverse lookup

Meaning:

IP address
    ↓
hostname

Example:

192.168.1.50
       ↓
PTR
       ↓
server.example.com

🧠 Memory Trick

PoinTeR points backward.

Normal:

Name → IP

PTR:

IP → Name

🚨 BIG EXAM DISTINCTION

A Record

NAME → IPv4

AAAA

NAME → IPv6

PTR

IP → NAME

This distinction is specifically called out as an exam trap in your chapter.

👑 SOA

SOA = Start of Authority

It contains:

Administrative information about the DNS zone.

Your chapter mentions things like:

• Zone administrator information

• Refresh information

• TTL

🧠 Memory

SOA = Starting information for the zone.

📝 TXT Record

A TXT record stores:

Text information

Your chapter specifically associates TXT with:

• SPF

• DKIM

• Mail authentication

• Anti-spam

🧠 Memory

TXT = TEXT

Very literal.

📍 SRV Record

SRV = Service Record

It identifies:

A service location + port number.

Example concept:

"Where is this service?"
        ↓
SRV
        ↓
Server + Port

🧠 Memory

SRV = SeRVice

🔐 CAA Record

CAA specifies:

Which Certificate Authorities may issue certificates for a domain.

🧠 Memory

CAA = Certificate Authority Allowed

Not the literal expansion — memory trick.

🔍 Forward Lookup

A forward lookup goes:

Name → IP

Example:

server.example.com
        ↓
192.168.1.50

A and AAAA records are used with forward lookups. Your source describes forward zones as name → IP.

🔄 Reverse Lookup

A reverse lookup goes:

IP → Name

Uses:

PTR

Example:

192.168.1.50
       ↓
server.example.com

Your chapter states that reverse zones hold PTR records.

💻 Knowt Notes — Deep Understanding

Why Does DNS Exist?

Imagine having to remember:

142.250.x.x
104.x.x.x
172.x.x.x

for every website.

That would be terrible.

Instead you remember:

google.com
youtube.com
amazon.com

DNS handles the translation.

YOU
 ↓
"Where is example.com?"
 ↓
DNS
 ↓
"Use this IP address."

🧠 Think of DNS Records as Different Contact Cards

Imagine a company's contact page.

A

"Where is the IPv4 address?"

AAAA

"Where is the IPv6 address?"

MX

"Who handles email?"

NS

"Who is the official DNS server?"

CNAME

"Does this name have an alias?"

PTR

"Who owns this IP?"

SRV

"Where is this service and what port?"

CAA

"Who is allowed to issue certificates?"

⭐ DNS Record Master Table

These are the high-yield DNS records listed in your Chapter 5 material.

🚨 Exam Traps

Trap #1

A = IPv6

❌ Wrong.

A = IPv4

AAAA = IPv6

Trap #2

PTR = Name → IP

❌ Wrong.

PTR is:

IP → Name

Trap #3

MX = DNS server

❌ Wrong.

MX:

Mail server

NS:

Name server

Trap #4

CNAME maps directly to an IP.

For this chapter, think:

CNAME = name alias to another name

Trap #5

DNS always uses TCP 53.

❌ Wrong.

Remember:

UDP 53 = queries

TCP 53 = zone transfers/updates

🎴 Flashcards

⭐ 1 — EXAM GOLD

What is the primary purpose of DNS?

A. Automatically assign IP addresses
B. Resolve names to IP addresses
C. Detect collisions
D. Encrypt Ethernet frames

✅ Correct: B

🧠 DNS = Internet phone book.

⭐ 2

Which port is normally used for DNS queries?

A. UDP 67
B. UDP 68
C. UDP 53
D. UDP 123

✅ Correct: C

⭐ 3

Which protocol/port is associated with DNS zone transfers in your chapter?

A. UDP 53
B. TCP 53
C. TCP 67
D. UDP 443

✅ Correct: B

⭐ 4 — EXAM GOLD

Which DNS record maps a hostname to an IPv4 address?

A. AAAA
B. PTR
C. A
D. MX

✅ Correct: C

🧠 A = Address = IPv4

⭐ 5

Which record maps a hostname to IPv6?

A. A
B. AAAA
C. PTR
D. NS

✅ Correct: B

⭐ 6

An administrator wants shop.example.com to be an alias for store.example.com.

Which record?

A. MX
B. PTR
C. CNAME
D. SOA

✅ Correct: C

⭐ 7 — EXAM GOLD

Which DNS record identifies the mail server responsible for a domain?

A. NS
B. MX
C. PTR
D. CNAME

✅ Correct: B

🧠 MX = Mail eXchanger

⭐ 8

Which record identifies a domain's authoritative name server?

A. MX
B. CNAME
C. NS
D. TXT

✅ Correct: C

⭐ 9 — EXAM GOLD

A technician knows an IP address and wants to determine its hostname.

Which DNS record is needed?

A. A
B. AAAA
C. PTR
D. MX

✅ Correct: C

🧠 PTR = IP → Name

⭐ 10

Which record contains administrative information about a DNS zone?

A. CNAME
B. MX
C. SOA
D. A

✅ Correct: C

11

Which record type is commonly used for SPF and DKIM information?

A. PTR
B. TXT
C. A
D. NS

✅ Correct: B

⭐ 12

Which DNS record identifies a service and port?

A. MX
B. SOA
C. SRV
D. CNAME

✅ Correct: C

🧠 SRV = SeRVice

13

Which record controls which certificate authorities may issue certificates for a domain?

A. PTR
B. MX
C. TXT
D. CAA

✅ Correct: D

⭐ 14 — EXAM TRAP

Which pairing is correct?

A. A → IPv6
B. AAAA → IPv4
C. PTR → IP to hostname
D. MX → authoritative DNS server

✅ Correct: C

⭐ 15

Which lookup direction represents a forward DNS lookup?

A. Hostname → IP address
B. IP address → hostname
C. MAC → IP
D. Port → hostname

✅ Correct: A

⭐ 16

Which lookup direction represents a reverse DNS lookup?

A. Hostname → IP
B. IP → hostname
C. MAC → IP
D. Domain → gateway

✅ Correct: B

🧠 Memory Board

📖 DNS Names ↔ IP information PORT 53 UDP = normal queries TCP = zone transfers A Name → IPv4 AAAA Name → IPv6 CNAME Alias / nickname MX Mail server NS Name server PTR IP → Name SOA Zone admin info TXT Text / SPF / DKIM SRV Service + port CAA Allowed certificate authority FORWARD Name → IP REVERSE IP → Name PTR

🎯 Network+ Summary

For this session, the biggest thing is learning the DNS records without mixing them up.

A = IPv4

AAAA = IPv6

CNAME = alias

MX = mail

NS = nameserver

PTR = reverse lookup

SOA = zone information

TXT = text/SPF/DKIM

SRV = service + port

CAA = certificate-authority permissions

And remember:

UDP 53 = normal DNS query

TCP 53 = zone transfer/update

Your chapter specifically lists DNS record types, forward/reverse zones, and UDP 53 as Network+ exam priorities.

Next in our Chapter 5 plan is Session 8 — DNS Part 2, where we get into forward/reverse zones, primary vs. secondary DNS, authoritative vs. non-authoritative, recursive vs. iterative, TTL, DNSSEC, DoH, DoT, and DoQ.