IPv6 Subnet Calculator
Documentation
2001:db8::/32RFC 3849 reserved for examples and documentation. Safe to print, never routed — the IPv6 equivalent of 192.0.2.0/24.
Not announced in BGP, so there is no operator or routing to show.
RFC 3849 reserved for examples and documentation. Safe to print, never routed — the IPv6 equivalent of 192.0.2.0/24.
2001:db8::
2001:0db8:0000:0000:0000:0000:0000:0000
2001:db8::
2001:db8:f:ffff:ffff:ffff:ffff:ffff
ffff:ffff:fff0::
/44
0.0.0.8.b.d.0.1.0.0.2.ip6.arpa
0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa
Network Information
1.93 × 10²⁵
1,048,576
2001:db8:: – 2001:db8:f:ffff:ffff:ffff:ffff:ffff
IPv6 Prefix Cheat Sheet
| Prefix | Addresses | /64 subnets | Netmask | Typical use |
|---|---|---|---|---|
| /128 | 1 | — | ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff | A single address — a host route or a loopback |
| /127 | 2 | — | ffff:ffff:ffff:ffff:ffff:ffff:ffff:fffe | Point-to-point link between two routers (RFC 6164) |
| /126 | 4 | — | ffff:ffff:ffff:ffff:ffff:ffff:ffff:fffc | Four addresses — the IPv4 /30 habit carried over to a router link |
| /124 | 16 | — | ffff:ffff:ffff:ffff:ffff:ffff:ffff:fff0 | 16 addresses — small static assignment |
| /120 | 256 | — | ffff:ffff:ffff:ffff:ffff:ffff:ffff:ff00 | 256 addresses — the IPv6 size of an IPv4 /24, used for static server ranges |
| /112 | 65,536 | — | ffff:ffff:ffff:ffff:ffff:ffff:ffff:0 | Sometimes used for numbered infrastructure links |
| /96 | 4,294,967,296 | — | ffff:ffff:ffff:ffff:ffff:ffff:: | Translation and mapping prefixes (::ffff:0:0/96, 64:ff9b::/96) sit here |
| /80 | 281,474,976,710,656 | — | ffff:ffff:ffff:ffff:ffff:: | Below the LAN boundary — breaks SLAAC, occasionally seen in labs |
| /64 | 1.84 × 10¹⁹ | 1 | ffff:ffff:ffff:ffff:: | One LAN. The standard subnet size, and the smallest that SLAAC works on |
| /60 | 2.95 × 10²⁰ | 16 | ffff:ffff:ffff:fff0:: | Smaller residential assignment — 16 /64 LANs |
| /56 | 4.72 × 10²¹ | 256 | ffff:ffff:ffff:ff00:: | The usual residential or small-business assignment — 256 /64 LANs |
| /52 | 7.55 × 10²² | 4,096 | ffff:ffff:ffff:f000:: | Nibble-aligned split of a site /48, tidy for reverse DNS |
| /48 | 1.2 × 10²⁴ | 65,536 | ffff:ffff:ffff:: | The standard site allocation — one organisation or campus, 65,536 /64s |
| /44 | 1.93 × 10²⁵ | 1,048,576 | ffff:ffff:fff0:: | Large enterprise or a POP inside an ISP |
| /40 | 3.09 × 10²⁶ | 16,777,216 | ffff:ffff:ff00:: | Aggregation boundary inside a large ISP; a nibble above /44 |
| /36 | 4.95 × 10²⁷ | 268,435,456 | ffff:ffff:f000:: | Regional slice of an ISP allocation |
| /32 | 7.92 × 10²⁸ | 4,294,967,296 | ffff:ffff:: | The standard ISP allocation — enough for 65,536 customer /48s |
| /29 | 6.33 × 10²⁹ | 34,359,738,368 | ffff:fff8:: | Common RIR allocation to an ISP, sized to allow later growth |
| /28 | 1.26 × 10³⁰ | 68,719,476,736 | ffff:fff0:: | Large ISP allocation from an RIR |
| /24 | 2.02 × 10³¹ | 1,099,511,627,776 | ffff:ff00:: | Very large ISP or national network allocation |
| /20 | 3.24 × 10³² | 17,592,186,044,416 | ffff:f000:: | Sub-allocation inside an RIR |
| /16 | 5.19 × 10³³ | 281,474,976,710,656 | ffff:: | Very large block; 2002::/16 (6to4) and ff00::/8's neighbours live at this scale |
| /12 | 8.3 × 10³⁴ | 4.5 × 10¹⁵ | fff0:: | An RIR's allocation from IANA |
| /10 | 3.32 × 10³⁵ | 1.8 × 10¹⁶ | ffc0:: | fe80::/10, link-local — every interface has one |
| /7 | 2.65 × 10³⁶ | 1.44 × 10¹⁷ | fe00:: | fc00::/7, the unique local (ULA) block |
| /3 | 4.25 × 10³⁷ | 2.3 × 10¹⁸ | e000:: | 2000::/3, the global unicast block the registries allocate from |
| /0 | 3.4 × 10³⁸ | 1.84 × 10¹⁹ | :: | Default route — matches every IPv6 address |
Quick Reference
How to Use
Enter an IPv6 address and prefix length above — or paste 2001:db8::/48 straight in — to see the prefix boundaries, how many /64s it holds, its reverse DNS zone, and what kind of address it is.
Why /64 Matters
A /64 is the standard IPv6 subnet, and the smallest one stateless autoconfiguration (SLAAC) works on: the low 64 bits are the interface identifier, which hosts assign themselves. Subnet above /64, never below it.
Common Prefix Sizes
/32 is a typical ISP allocation, /48 goes to a site or organisation, /56 to a home or small business, and /64 to a single LAN. Router-to-router links usually use /127.