Who uses a /12 in IPv6?

IANA allocates /12 blocks to the Regional Internet Registries. Each RIR then suballocates smaller blocks (commonly /32 to /48) to ISPs and large organizations in its region.

What is the difference between /12 and /13?

A /12 is twice as large as /13. /12 has 2¹¹⁶ addresses; /13 has 2¹¹⁵. Each step down the prefix number doubles the address count.

How does /12 compare to /11?

A /11 is twice as large as /12. Moving from /12 to /11 adds one more fixed network bit, halving the host portion from 2¹¹⁶ to 2¹¹⁷ addresses.

How do I calculate an IPv6 /12 subnet?

Enter an IPv6 address and select prefix /12 in the calculator above — or paste full CIDR notation like 2001::/12. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹¹⁶ addresses.

IPv6 /12 Subnet Calculator

Results update as you type

A /12 is the typical block a Regional Internet Registry (RIR) like ARIN, RIPE, or APNIC receives from IANA. For example, 2400::/12 is allocated to APNIC. A /12 contains 2¹¹⁶ addresses, enough for the RIR to suballocate millions of /32s to ISPs.

Prefix length

/128

/12 = 2¹¹⁶ addresses (≈ 8.31 × 10³⁴)

Results for 2000::/12

Global UnicastGlobal scope

Network / prefixThe first address — identifies the subnet itself

First addressSubnet-router anycast; first address in the block

Last addressThe highest address in this block

Prefix maskEquivalent to /12

Total addresses≈ 8.31 × 10³⁴ addresses

Address typeGlobally routable scope

More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown

Neighboring /12 subnets

Expanded address
Compressed address
Network (expanded)
Last address (expanded)
Prefix mask
Total addresses (exact)
Reverse DNS (PTR)
Host bits / network bits

Hextet breakdown

20010000000000000000000000000000

NetworkSplit groupHost

Quick facts for IPv6 /12

Prefix mask: fff0::
Total addresses: 2¹¹⁶
Approx. count: 8.31 × 10³⁴
/64 subnets: 2⁵²

IPv6 /12 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

mixhosthosthosthosthosthosthost

Network bits (12)Split hextetHost bits (116)

Network bits: 12
Host bits: 116
Prefix mask: fff0::
Total addresses: 2¹¹⁶
Approx. count: 8.31 × 10³⁴
/64 subnets: 2⁵²
Addresses formula: 2^116
/64 relationship: 2⁵² × /64 subnets

Overview

Common use cases

IANA-to-RIR allocations
Top-level address-space planning

Key facts

A /12 fixes 12 network bits and leaves 116 host bits — 2¹¹⁶ total addresses.
In network design terms, /12 is typically a RIR-level aggregation block.
You can subnet a /12 into about 2⁵² /64 LANs.
At site scale, /12 equals about 2³⁶ /48 allocations.
At ISP scale, /12 contains 2²⁰ /32 blocks.

Design guidance

A /12 belongs in BGP aggregation and RIR allocation planning — not on a VLAN interface. If you are subnetting for a real deployment, work downward: carve /48 or /56 site blocks first, then assign one /64 per LAN. Announcing a single aggregated /12 (or larger) upstream keeps global routing tables manageable.

Practical example

An ISP holding 2001::/12 might announce the entire /12 to upstream providers as one BGP route, then delegate /48 blocks such as 2001:db8:0001::/48 and 2001:db8:0002::/48 to business customers. Each customer subnets their /48 into /64 LANs.

Related RFCs and standards

RFC 4291IPv6 Addressing Architecture
RFC 3849IPv6 Documentation Address Prefix (2001:db8::/32)

Prefix sizing reference

Divide /12 into…

Prefix	Subnets	Addresses each
/13	2	2¹¹⁵
/14	4	2¹¹⁴
/16	16	2¹¹²
/20	256	2¹⁰⁸

/12 fits inside…

Supernet	Addresses	/12s inside
/11	2¹¹⁷	2
/10	2¹¹⁸	4
/8	2¹²⁰	16
/4	2¹²⁴	256

Notable /12 networks

2400::/12APNIC
2600::/12ARIN
2a00::/12RIPE NCC
2001:db8::/32Documentation prefix (RFC 3849)

Frequently asked questions

Common questions about IPv6 /12 blocks, prefix sizes, and use cases.

Common IPv6 prefix sizes

/3 /12 /16 /20 /24 /28 /32 /36 /40 /44 /48 /52 /56 /60 /64 /80 /96 /112 /120 /124 /126 /127 /128