How many addresses are in an IPv6 /47?

An IPv6 /47 contains 2⁸¹ addresses. The prefix fixes the first 47 bits; the remaining 81 bits identify individual addresses in the block.

How many /64 subnets fit in a /47?

A /47 can be divided into 2¹⁷ standard /64 LAN subnets. Each /64 holds 2⁶⁴ addresses, so the combined block is effectively inexhaustible for normal use.

How many /48 site allocations are in a /47?

A /47 contains 2¹ /48 site allocations. A /48 is the classic size assigned to a business site or campus.

When would an organization receive a /47?

A /47 is assigned when an organization needs more address space than a single /48 but does not qualify for a full ISP-style /32. It is common for large enterprises with many branch offices.

What is the difference between /47 and /48?

A /47 is twice as large as /48. /47 has 2⁸¹ addresses; /48 has 2⁸⁰. Each step down the prefix number doubles the address count.

How does /47 compare to /46?

A /46 is twice as large as /47. Moving from /47 to /46 adds one more fixed network bit, halving the host portion from 2⁸¹ to 2⁸² addresses.

IPv6 /47 Subnet Calculator

Results update as you type

A /47 block fixes the first 47 bits of the address, leaving 81 host bits and 2⁸¹ total addresses. It subdivides into 2¹⁷ /64 LAN subnets. That is also 2¹ /48 site allocations. A /47 sits between the standard ISP /32 and the site /48 — useful when an organization needs more than one /48 but less than a full /32.

Prefix length

/128

/47 = 2⁸¹ addresses (≈ 2.42 × 10²⁴)

Results for 2001:db8:abcc::/47

Documentation (RFC 3849)Global 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 /47

Total addresses≈ 2.42 × 10²⁴ addresses

Address typeGlobally routable scope

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

Neighboring /47 subnets

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

Hextet breakdown

20010db8abcd00000000000000000000

NetworkSplit groupHost

Quick facts for IPv6 /47

Prefix mask: ffff:ffff:fffe::
Total addresses: 2⁸¹
Approx. count: 2.42 × 10²⁴
/64 subnets: 2¹⁷

IPv6 /47 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

netnetmixhosthosthosthosthost

Network bits (47)Split hextetHost bits (81)

Network bits: 47
Host bits: 81
Prefix mask: ffff:ffff:fffe::
Total addresses: 2⁸¹
Approx. count: 2.42 × 10²⁴
/64 subnets: 2¹⁷
Addresses formula: 2^81
/64 relationship: 2¹⁷ × /64 subnets

Overview

Common use cases

Enterprise or ISP allocations above site size
Multi-site organizations needing several /48s
Address renumbering and growth planning

Key facts

A /47 fixes 47 network bits and leaves 81 host bits — 2⁸¹ total addresses.
In network design terms, /47 is typically a enterprise or multi-site allocation.
You can subnet a /47 into 2¹⁷ /64 LANs.
At site scale, /47 equals 2¹ /48 allocations.

Design guidance

A /47 suits organizations that have outgrown a single /48 but do not need a full /32 ISP allocation. Plan your addressing scheme before delegating: assign one /48 (or smaller) per major site, then subnet each site into /64 LANs. Document your nibble boundaries so future growth does not force renumbering.

Practical example

An ISP holding 2001:db8:abcd::/47 might announce the entire /47 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

Prefix sizing reference

Divide /47 into…

Prefix	Subnets	Addresses each
/48	2	2⁸⁰
/49	4	2⁷⁹
/51	16	2⁷⁷
/55	256	2⁷³

/47 fits inside…

Supernet	Addresses	/47s inside
/46	2⁸²	2
/45	2⁸³	4
/43	2⁸⁵	16
/39	2⁸⁹	256

Frequently asked questions

Common questions about IPv6 /47 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