IPv6 Subnet Cheat Sheet
Quick reference for IPv6 prefix lengths, address capacity, and standard allocation sizes.
| Prefix | Total Addresses | /64 Subnets | Common Use |
|---|---|---|---|
| /128 | 20 | — | Single host, loopback (::1) |
| /127 | 21 | — | Point-to-point links (RFC 6164) |
| /126 | 22 | — | Point-to-point links (4 addresses) |
| /112 | 216 | — | 65,536 addresses — rare, but valid |
| /96 | 232 | — | Legacy IPv4-mapped space |
| /80 | 248 | — | Large host-address space |
| /64 | 264 | 1 /64 | Standard LAN — required for SLAAC |
| /63 | 265 | 2^1 | Two /64 subnets |
| /62 | 266 | 2^2 | Four /64 subnets |
| /60 | 268 | 2^4 | 16 /64 subnets (common delegated size) |
| /56 | 272 | 2^8 | 256 /64 subnets (common residential delegation) |
| /52 | 276 | 2^12 | 4,096 /64 subnets |
| /48 | 280 | 2^16 | 65,536 /64 subnets — typical site allocation |
| /44 | 284 | 2^20 | 1,048,576 /64 subnets |
| /40 | 288 | 2^24 | 16,777,216 /64 subnets |
| /36 | 292 | 2^28 | 268,435,456 /64 subnets |
| /32 | 296 | 2^32 | Typical ISP allocation from an RIR |
| /24 | 2104 | 2^40 | Very large provider or registry allocation |
| /20 | 2108 | 2^44 | Large regional allocation |
| /16 | 2112 | 2^48 | Very large allocation |
| /12 | 2116 | 2^52 | Very large allocation |
| /8 | 2120 | 2^56 | Major address-space block |
| /4 | 2124 | 2^60 | Major IANA-designated block |
| /0 | 2128 | 2^64 | Default route — all IPv6 addresses |
Why is /64 so important in IPv6?
The /64 prefix is the foundational building block of IPv6 networking. Stateless Address Autoconfiguration (SLAAC) uses a 64-bit interface-identifier field, so general-purpose LAN segments are normally assigned a /64. A /64 contains 264 addresses, or about 18.4 quintillion.
Standard ISP Allocation Sizes
Common delegation and allocation sizes include:
- /48 — Common end-site allocation, providing 65,536 /64 subnets.
- /56 — Common residential or small-site delegation, providing 256 /64 subnets.
- /60 — Smaller delegation, providing 16 /64 subnets.
- /32 — Common RIR allocation size for an ISP or network operator.
Common Reserved IPv6 Prefixes
These prefixes have assigned meanings and are not ordinary global-unicast space:
::1/128— Loopback.fe80::/10— Link-local unicast.fc00::/7— Unique Local Addresses (ULA).2001:db8::/32— Documentation and examples.2002::/16— 6to4 transition prefix.ff00::/8— Multicast.