Internet Protocol version 6 (IPv6)¶

Advantages of IPv6 deployment¶

Vast Address Space: 128-bit addresses (≈3.4×10³⁸ addresses) eliminate scarcity.
Simplified Header: streamlined base header improves router processing efficiency.
Stateless Address Autoconfiguration (SLAAC): hosts can self-configure addresses without DHCP.
Built-in Security: IPsec (authentication/encryption) is mandatory, enhancing end-to-end security.
Improved Multicast and Anycast: efficient group communication and service delivery.
No NAT Required: restores end-to-end connectivity, simplifying applications.
Better Mobility Support: Mobile IPv6 handles roaming more effectively.

Compression: remove leading zeros in each hextet (16-bit block) and replace the longest consecutive sequence of all-zero hextets with :: (once per address).
- Example: 2001:0db8:0000:130f:0000:0000:08ec:140b → 2001:db8:0:130f::8ec:140b
Lowercase: use lowercase letters (e.g., fd00::1, not FD00::1).
CIDR Notation: always include prefix length (e.g., 2001:db8::/32).

Type	Prefix	Scope	Use Case
Global Unicast	`2000::/3`	Global (internet)	Public addresses, routable worldwide.
Unique Local (ULA)	`fd00::/8`	Site-local (private)	Internal networks (not routable online).
Link-Local	`fe80::/10`	Link-local (same subnet)	Neighbour Discovery, SLAAC.
Multicast	`ff00::/8`	Varies (e.g., `ff02::` = link)	Group communication (e.g., `ff02::1` = all nodes).
Loopback	`::1/128`	Node-local	Localhost.
Unspecified	`::/128`	None	Absence of address (e.g., DAD).

Subnetting borrows bits from the host portion to create subnets.
Formula: Number of subnets = 2^(new_prefix - current_prefix)
Example: how many /64 subnets in a /56? 2^(64-56) = 2^8 = 256 subnets.
Subnet ranges:
- Base: 2001:db8:abc::/56
- Subnet 1: 2001:db8:abc:0::/64
- Subnet 2: 2001:db8:abc:1::/64
- Subnet 256: 2001:db8:abc:ff::/64

NDP (Neighbour Discovery Protocol): replaces ARP, manages neighbour reachability.
SLAAC (Stateless Address Autoconfiguration): hosts generate addresses using RA messages.
DHCPv6: stateful address and config assignment (complements SLAAC).
ICMPv6: error reporting and diagnostic functions (e.g., ping6).
PMTUD (Path MTU Discovery): determines optimal packet size for a path.

Characteristics:
- No broadcast (uses multicast).
- Extension headers for optional features.
- Simplified fragmentation (handled by source).
Security Concerns:
- RA Guard: needed to block rogue Router Advertisements.
- DHCPv6 Spoofing: attackers may impersonate DHCPv6 servers.
- Extension Header Attacks: can be used to evade firewalls.
- Privacy Extensions: temporary addresses mitigate tracking.
- Address Scanning: large address space makes reconnaissance difficult.

Dual Stack: run IPv4 and IPv6 simultaneously on devices.
Tunneling: encapsulate IPv6 in IPv4 (e.g., 6in4, GRE).
Translation: convert between v4 and v6 (e.g., NAT64, SIIT).
Proxying: use a proxy for protocol translation.
464XLAT: allows IPv4-only apps to work in an IPv6 network (common in mobile networks).