How many addresses are in an IPv6 /45?

An IPv6 /45 contains 2⁸³ addresses. The prefix fixes the first 45 bits; the remaining 83 bits identify individual addresses in the block.

How many /64 subnets fit in a /45?

A /45 can be divided into 2¹⁹ 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 /45?

A /45 contains 2³ /48 site allocations. A /48 is the classic size assigned to a business site or campus.

When would an organization receive a /45?

A /45 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 /45 and /46?

A /45 is twice as large as /46. /45 has 2⁸³ addresses; /46 has 2⁸². Each step down the prefix number doubles the address count.

How does /45 compare to /44?

A /44 is twice as large as /45. Moving from /45 to /44 adds one more fixed network bit, halving the host portion from 2⁸³ to 2⁸⁴ addresses.

IPv6 /45 Subnet Calculator

Results update as you type

A /45 block fixes the first 45 bits of the address, leaving 83 host bits and 2⁸³ total addresses. It subdivides into 2¹⁹ /64 LAN subnets. That is also 2³ /48 site allocations. A /45 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

/45 = 2⁸³ addresses (≈ 9.67 × 10²⁴)

Results for 2001:db8:abc8::/45

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 /45

Total addresses≈ 9.67 × 10²⁴ addresses

Address typeGlobally routable scope

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

Neighboring /45 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 /45

Prefix mask: ffff:ffff:fff8::
Total addresses: 2⁸³
Approx. count: 9.67 × 10²⁴
/64 subnets: 2¹⁹

IPv6 /45 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

netnetmixhosthosthosthosthost

Network bits (45)Split hextetHost bits (83)

Network bits: 45
Host bits: 83
Prefix mask: ffff:ffff:fff8::
Total addresses: 2⁸³
Approx. count: 9.67 × 10²⁴
/64 subnets: 2¹⁹
Addresses formula: 2^83
/64 relationship: 2¹⁹ × /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 /45 fixes 45 network bits and leaves 83 host bits — 2⁸³ total addresses.
In network design terms, /45 is typically a enterprise or multi-site allocation.
You can subnet a /45 into 2¹⁹ /64 LANs.
At site scale, /45 equals 2³ /48 allocations.

Design guidance

A /45 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::/45 might announce the entire /45 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 /45 into…

Prefix	Subnets	Addresses each
/46	2	2⁸²
/47	4	2⁸¹
/49	16	2⁷⁹
/53	256	2⁷⁵

/45 fits inside…

Supernet	Addresses	/45s inside
/44	2⁸⁴	2
/43	2⁸⁵	4
/41	2⁸⁷	16
/37	2⁹¹	256

Frequently asked questions

Common questions about IPv6 /45 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