IPv4 and IPv6

IPv4

• 32-bit address → 2³² = ~4.3 billion addresses.
• Written in dotted decimal: 192.168.1.1
• 4 octets, each 0–255.
• Header size: 20–60 bytes.

IPv4 Header Key Fields

• Version (4 bits) — value = 4
• TTL — prevents infinite loops, decremented at each hop
• Protocol — TCP=6, UDP=17, ICMP=1
• Source/Destination IP
• Checksum — error checking

Address Classes (Classful — mostly obsolete)

Class	Range	Use
A	1.0.0.0 – 126.x.x.x	Large networks
B	128.0.0.0 – 191.255.x.x	Medium networks
C	192.0.0.0 – 223.255.255.x	Small networks
D	224.0.0.0 – 239.x.x.x	Multicast
E	240.0.0.0 – 255.x.x.x	Reserved

Private IP Ranges (RFC 1918)

Range	CIDR
10.0.0.0 – 10.255.255.255	10.0.0.0/8
172.16.0.0 – 172.31.255.255	172.16.0.0/12
192.168.0.0 – 192.168.255.255	192.168.0.0/16

Special Addresses

• 127.0.0.1 → Loopback
• 0.0.0.0 → Default route / unspecified
• 255.255.255.255 → Limited broadcast

IPv4 Notation Explained

192       . 168      . 1        . 1
11000000    10101000   00000001   00000001

Each octet = 8 bits (decimal 0–255). Total = 32 bits.

IPv6

• 128-bit address → 2¹²⁸ = ~340 undecillion addresses.
• Written in colon-hex: 2001:0db8:85a3:0000:0000:8a2e:0370:7334

IPv6 Compression Rules

• Leading zeros dropped: 0db8 → db8
• Consecutive all-zero groups → :: (only once)
• Example: 2001:db8::8a2e:370:7334

IPv6 Header (Fixed 40 bytes — simpler than IPv4)

• Version (4 bits) — value = 6
• Traffic Class — like DSCP/ToS in IPv4
• Flow Label — identifies packet flows for QoS
• Hop Limit — like TTL
• No checksum — offloaded to transport layer

IPv6 Address Types

Type	Description	Example
Unicast	One-to-one	2001:db8::1
Multicast	One-to-many	FF02::1
Anycast	One-to-nearest	Same as unicast format
No Broadcast	Replaced by multicast	—

Special IPv6 Addresses

• ::1 → Loopback (equivalent to 127.0.0.1)
• FE80::/10 → Link-local (auto-configured, not routable)
• :: → Unspecified

Key Improvements of IPv6 over IPv4

• No NAT needed — every device gets a global address
• No ARP — replaced by NDP (Neighbor Discovery Protocol)
• Auto-configuration — SLAAC (Stateless Address Autoconfiguration)
• Built-in IPSec support
• Simpler header — faster routing
• No broadcast — reduces unnecessary traffic

IPv6 Notation Explained

2001 : 0db8 : 85a3 : 0000 : 0000 : 8a2e : 0370 : 7334
16b    16b    16b    16b    16b    16b    16b    16b   = 128 bits total

IPv4 vs IPv6 — Side by Side

Feature	IPv4	IPv6
Address size	32-bit	128-bit
Address count	~4.3 billion	~340 undecillion
Header size	20–60 bytes (variable)	40 bytes (fixed)
Checksum	Yes	No
Broadcast	Yes	No (multicast instead)
ARP	Yes	No (NDP instead)
NAT required	Yes (usually)	No
Configuration	Manual / DHCP	SLAAC / DHCPv6
Security	Optional IPSec	Built-in IPSec
Notation	Dotted decimal	Colon hexadecimal
Groups	4 octets (8 bits)	8 groups (16 bits)
Display format	Decimal	Hexadecimal