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Master modern IPv6 network design: understand address types, prefix allocation (/48 vs /56 vs /64), address compression rules, and reverse PTR setup.
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IPv6 addresses comprise 128 binary bits, organized into eight 16-bit hexadecimal blocks (hexadectets) separated by colons. Unlike IPv4's 4.3 billion address pool, IPv6 delivers 340 undecillion (3.4 × 10^38) addresses, eliminating the need for NAT (Network Address Translation).
RFC 5952 establishes standard canonical text rules: leading zeros within a block must be omitted, lowercase hexadecimal characters must be used, and a single double-colon (::) must compress the longest run of consecutive 16-bit zero fields.
In IPv6, subnetting does not focus on conserving host addresses; it focuses on logical hierarchy. The first 64 bits represent the Network Prefix, and the remaining 64 bits represent the Interface Identifier (host address).
• /32: Standard ISP allocation from Regional Internet Registries (RIRs). • /48: Standard enterprise site allocation (providing 65,536 separate /64 subnets). • /56: Standard residential broadband delegation (providing 256 /64 subnets). • /64: Mandatory single LAN subnet size required for SLAAC (Stateless Address Autoconfiguration).
| Prefix | Total /64 Subnets | Typical Allocation Entity |
|---|---|---|
| /32 | 4,294,967,296 | Tier-1 & Tier-2 ISPs |
| /48 | 65,536 | Enterprise Datacenters & Campuses |
| /56 | 256 | Small Businesses & Residential Broadband |
| /64 | 1 | Single VLAN, Wi-Fi Network, or LAN Segment |
Every IPv6-enabled interface automatically configures multiple IP addresses with different scopes:
1. Global Unicast (2000::/3): Publicly routable internet addresses. 2. Link-Local (fe80::/10): Automatically configured on every interface, valid only within the immediate local physical or wireless link. Used for router discovery and neighbor solicitation. 3. Unique Local (fc00::/7): Private routable enterprise addresses (the IPv6 equivalent of RFC 1918 private IPv4 space).
Configuring a LAN subnet smaller than /64 (such as /80 or /112) breaks SLAAC, mobile IPv6, and standard hardware routing tables. Subnet allocation in IPv6 should always terminate at /64 for end-user networks.
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