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IPv4 and IPv6 Addressing

IPv4 and IPv6 Addressing — Notes, Classes, Ports & MCQs | GyanDesk
Computer Networks · Exam Notes

IPv4 and IPv6 Addressing — Complete Study Notes with MCQs

Exam-focused notes on IPv4 and IPv6 addressing for SSC, Banking (IBPS/SBI), Railway, UPSC, NIELIT, JAIIB/CAIIB and IT officer papers. Learn bits, classes, private ranges, special addresses, CIDR basics, IPv6 types, transition methods, and practice with interactive MCQs.

IPv4 32-bit IPv6 128-bit Classes A–E 60 practice MCQs

What is an IP Address?

Core definition asked in almost every computer awareness paper

Must Know

An IP address (Internet Protocol address) is a logical address that identifies a device (or interface) on a network so that data can be sent to the correct destination — like a house number for computers.

Why it matters
Without IP addressing, routers and hosts cannot route packets between networks. Exams ask bits, format, classes, private ranges, and IPv4 vs IPv6 differences.
Two versions
IPv4 (older, 32-bit) and IPv6 (newer, 128-bit). Both can run together using dual-stack.
Exam line: IP address = unique logical identity of a host on an IP network. MAC address = physical/hardware identity on a LAN.

IPv4

32 bits · dotted decimal · ~4.3 billion addresses · still widely used

IPv6

128 bits · colon hex · huge address space · designed for growth

Related ideas

Subnetting, CIDR, NAT, DHCP, DNS, dual-stack, tunneling

IPv4 Addressing

32-bit addresses in four octets

Very Important

IPv4 uses a 32-bit address written as four decimal numbers (octets) separated by dots — dotted decimal notation.

Key facts

  • Format example: 192.168.1.1
  • Each octet: 0 to 255
  • Total bits: 4 × 8 = 32
  • Total addresses: 232 ≈ 4.3 billion
  • Split into Network ID + Host ID

Exam hot points

  • Invalid if any part > 255 (e.g., 10.0.0.256)
  • Dotted decimal = IPv4
  • Colon hex = IPv6
  • IPv4 shortage led to NAT + IPv6
Memory tip: IPv4 = 4 numbers with dots. IPv6 = longer hex with colons.

IPv4 Address Classes (Classful)

Still heavily tested even though modern networks use CIDR

Class First octet Default mask Typical use Exam note
A 1 – 126 255.0.0.0 (/8) Very large networks 127 is loopback, not Class A hosts
B 128 – 191 255.255.0.0 (/16) Medium networks Common enterprise ranges
C 192 – 223 255.255.255.0 (/24) Small networks / LANs 192.168.x.x is Class C private
D 224 – 239 — Multicast Not for normal host unicast
E 240 – 255 — Experimental / research Reserved

Class A example

10.1.2.3 — first octet 10 → Class A

Class B example

172.16.5.10 — first octet 172 → Class B

Class C example

192.168.1.1 — first octet 192 → Class C

Quick test: Look only at the first octet to decide class in most MCQs.

Special, Private & Reserved IPv4 Addresses

High-frequency match-the-following style questions

Memorise

Special addresses

Loopback

  • 127.0.0.1 (and whole 127.0.0.0/8)
  • Tests the local host (localhost)

Limited broadcast

  • 255.255.255.255
  • Broadcast on the local network

APIPA / link-local

  • 169.254.0.0 – 169.254.255.255
  • Auto IP when DHCP fails

0.0.0.0

  • “This host” / unspecified / default route contexts
  • Meaning depends on use (binding vs routing)

Private IPv4 (RFC 1918)

Not routed on the public Internet. Used inside homes, offices, campuses. Public access usually needs NAT.

Range CIDR Class feel
10.0.0.0 – 10.255.255.255 10.0.0.0/8 Class A private
172.16.0.0 – 172.31.255.255 172.16.0.0/12 Class B private block
192.168.0.0 – 192.168.255.255 192.168.0.0/16 Class C private
Trap: 11.0.0.0/8 is not private. Only 10/8, 172.16/12, 192.168/16.

CIDR & Subnetting Basics (Exam Level)

Enough for competitive exams — not full engineering depth

Subnetting divides a large network into smaller networks. CIDR (Classless Inter-Domain Routing) writes the prefix length after a slash, e.g. 192.168.1.0/24.

/24 meaning

  • 24 network bits
  • 8 host bits
  • Mask: 255.255.255.0
  • Usable hosts: 254

/26 meaning

  • 26 network bits
  • Mask: 255.255.255.192
  • 64 addresses total
  • 62 usable hosts

/30 meaning

  • Often point-to-point links
  • 4 addresses total
  • 2 usable hosts
  • Mask: 255.255.255.252
Formula: Total addresses = 2(32 − prefix). Usable hosts ≈ total − 2 (network + broadcast) for normal IPv4 subnets.
Prefix Subnet mask Host bits Usable hosts (typical)
/8255.0.0.02416,777,214
/16255.255.0.01665,534
/24255.255.255.08254
/25255.255.255.1287126
/26255.255.255.192662
/27255.255.255.224530
/28255.255.255.240414
/30255.255.255.25222

IPv6 Addressing

128-bit addresses written in hexadecimal

Very Important

IPv6 uses 128 bits, written as eight groups of hexadecimal digits separated by colons. It was created mainly to solve IPv4 address exhaustion.

Key facts

  • Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
  • 8 hextets × 16 bits = 128 bits
  • Address space: 2128 (huge)
  • No broadcast (uses multicast/anycast)
  • IPsec support designed into architecture

Compression rules

  • Drop leading zeros in a group: 0db8 → db8
  • Replace one run of zero groups with ::
  • :: can appear only once
  • Example: 2001:0db8:0000:0000:0000:0000:0000:0001 → 2001:db8::1
Invalid tricks: 2001:::1 (triple colon) and two :: in one address are wrong.

IPv6 Address Types & Important Prefixes

Type Prefix / example Meaning
Global unicast 2000::/3 (e.g. 2001:db8::1) Publicly routable global addresses
Link-local fe80::/10 Auto on each interface; same link only
Unique local (ULA) fc00::/7 (often fd00::/8) Private-like internal addresses
Multicast ff00::/8 (e.g. ff02::1) One-to-many; replaces broadcast role
Loopback ::1 Like 127.0.0.1
Unspecified :: Like 0.0.0.0 in some contexts
Anycast Same as unicast format Nearest of multiple destinations

Unicast

One-to-one delivery to a single interface.

Multicast

One-to-many delivery to a group of interfaces.

Anycast

One-to-nearest among several hosts sharing the address.

Structure tip: Many IPv6 unicast addresses use 64-bit prefix + 64-bit interface ID.

IPv4 vs IPv6 — Comparison Table

Night-before-exam revision gold

Feature IPv4 IPv6
Address size 32 bits 128 bits
Notation Dotted decimal (192.0.2.1) Colon hexadecimal (2001:db8::1)
Address space ~4.3 billion 2128 (vast)
Broadcast Yes No (multicast/anycast)
Configuration Manual / DHCP common SLAAC + DHCPv6 options
Security IPsec optional/add-on IPsec support designed in
NAT need Common due to scarcity Much less needed
ARP ARP for IP→MAC Neighbor Discovery (NDP)
Header More complex / variable options Simpler fixed base header + extensions
Not a difference: Both can still use TCP/UDP at the transport layer. “TCP only works on IPv4” is false.

Moving from IPv4 to IPv6

Three transition words every exam loves

1 Dual-stack

Device/network runs both IPv4 and IPv6 at the same time. Most practical migration path.

2 Tunneling

Carry IPv6 packets inside IPv4 (or vice versa) across a network that does not natively support the inner protocol.

3 Translation

Convert between IPv4 and IPv6 traffic (e.g. NAT64) so IPv6-only and IPv4-only systems can talk.

Related exam concepts

NAT

  • Network Address Translation
  • Shares scarce public IPv4 addresses
  • Common in home/office routers
  • Less critical in pure IPv6 designs

Protocols over IP

  • TCP — reliable transport
  • UDP — fast, connectionless
  • ICMP / ICMPv6 — errors, ping, NDP helpers

One-Glance Quick Revision

IPv4 bits

32 bits · 4 octets · dotted decimal

IPv6 bits

128 bits · 8 hextets · colon hex

IPv4 total

~4.3 billion addresses

Class A / B / C

1–126 · 128–191 · 192–223

Class D / E

Multicast · Experimental

Private IPv4

10/8 · 172.16/12 · 192.168/16

Loopback

IPv4 127.0.0.1 · IPv6 ::1

APIPA

169.254.0.0/16

IPv6 link-local

fe80::/10

IPv6 multicast

ff00::/8

IPv6 global

2000::/3

IPv6 ULA

fc00::/7

/24 usable

254 hosts

/30 usable

2 hosts

No broadcast in

IPv6

Transition 3

Dual-stack · Tunnel · Translate

Practice MCQs on IPv4 & IPv6 Addressing

Tap any option to reveal the correct answer and a short explanation. Answers stay hidden until you choose.

60 Questions
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Exam Tips for IP Addressing Questions

First octet decides class

For classful MCQs, ignore the rest of the address until you classify A/B/C/D/E from the first number.

Dots vs colons

Dots + decimal = IPv4. Colons + hex = IPv6. Instant elimination tool.

Private ranges trio

Memorise 10/8, 172.16–31, 192.168/16. Anything else is usually public or special.

Loopback pair

127.0.0.1 ↔ ::1 is a favourite matching question.

Usable hosts formula

2^(host bits) − 2. For /24 → 2^8 − 2 = 254. For /30 → 2^2 − 2 = 2.

IPv6 has no broadcast

If an option says IPv6 broadcast like 255.255.255.255, it is wrong. Use multicast/anycast language.

GyanDesk tip: Revise classes + private ranges + IPv4 vs IPv6 table first, then attempt “High probability” MCQs. Related notes: Classful & CIDR · Subnetting · Common Protocols · Network Topologies · ARP & RARP · All IT notes

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