RFC 5952 • 128-BIT NEXT-GEN NETWORKING

IPv6 CIDR Subnet Calculator

Calculate IPv6 subnet boundaries, perform canonical RFC 5952 address compression and 32-character hexadecimal expansion, and compute total host allocations for cloud VPCs and ISP routing.

IPv6 Address (Compressed or Expanded)

Prefix Length

Canonical Compressed (RFC 5952)

2001:db8:85a3::8a2e:370:7334

Address Scope / Classification

Global Unicast (2000::/3)

Fully Expanded 128-bit Address

2001:0db8:85a3:0000:0000:8a2e:0370:7334

Subnet Network Prefix

2001:db8:85a3::/64

Start Address (Network)

2001:0db8:85a3:0000:0000:0000:0000:0000

End Address (Highest)

2001:0db8:85a3:0000:ffff:ffff:ffff:ffff

Total Assignable IP Addresses ($2^{128-n}$)

18,446,744,073,709,551,616 Addresses (18.4 Quintillion)

Mastering IPv6 Subnetting & Prefix Delegation

With IPv4 exhaustion an established reality, global cloud infrastructure relies on IPv6's massive 128-bit address space ($3.4 \times 10^{38}$ total addresses). Understanding standard allocation practices is vital for modern cloud architecture:

1. Why /64 is the Universal Standard Subnet

In IPv6, a single LAN or VPC subnet is almost always allocated a /64 prefix. This leaves 64 bits for the interface ID, which is mandatory for Stateless Address Autoconfiguration (SLAAC - RFC 4862). Even if a network only has 10 devices, allocating a /64 ensures compatibility with all routers and operating systems.

2. Standard Prefix Hierarchy

/32: Standard allocation granted to an Internet Service Provider (ISP) or large cloud provider.
/48: Standard allocation assigned to an entire enterprise organization or corporate campus (providing 65,536 individual /64 subnets).
/56: Standard allocation assigned by residential ISPs to home fiber connections (providing 256 individual /64 subnets).

3. Address Compression Rules (RFC 5952)

Leading zeroes within a 16-bit block are omitted (e.g. :0db8: becomes :db8:). A single contiguous sequence of all-zero blocks is replaced with a double colon (::). The double colon can only appear once in an address to avoid ambiguity.