How many addresses are in an IPv6 /27?

An IPv6 /27 contains 2¹⁰¹ addresses. The prefix fixes the first 27 bits; the remaining 101 bits identify individual addresses in the block.

How many /64 subnets fit in a /27?

A /27 can be divided into 2³⁷ 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 /27?

A /27 contains 2²¹ /48 site allocations. A /48 is the classic size assigned to a business site or campus.

What is the difference between /27 and /28?

A /27 is twice as large as /28. /27 has 2¹⁰¹ addresses; /28 has 2¹⁰⁰. Each step down the prefix number doubles the address count.

How does /27 compare to /26?

A /26 is twice as large as /27. Moving from /27 to /26 adds one more fixed network bit, halving the host portion from 2¹⁰¹ to 2¹⁰² addresses.

Is IPv6 /27 the same as IPv4 /27?

No. IPv4 /27 has at most a few thousand hosts. IPv6 /27 still contains 2¹⁰¹ addresses — an aggregation size in the IPv6 hierarchy, not a LAN subnet. IPv6 LANs are almost always /64.

IPv6 /27 Subnet Calculator

Results update as you type

A /27 block fixes the first 27 bits of the address, leaving 101 host bits and 2¹⁰¹ total addresses. It subdivides into about 2³⁷ /64 LAN subnets. That is also about 2²¹ /48 site allocations. At the ISP tier, a /27 holds 2⁵ /32 ISP blocks. Prefixes in this range appear in BGP tables and RIR allocation policies as aggregation blocks above the standard ISP /32.

Prefix length

/128

/27 = 2¹⁰¹ addresses (≈ 2.54 × 10³⁰)

Results for 2001:da0::/27

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 /27

Total addresses≈ 2.54 × 10³⁰ addresses

Address typeGlobally routable scope

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

Neighboring /27 subnets

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

Hextet breakdown

20010db8000000000000000000000000

NetworkSplit groupHost

Quick facts for IPv6 /27

Prefix mask: ffff:ffe0::
Total addresses: 2¹⁰¹
Approx. count: 2.54 × 10³⁰
/64 subnets: 2³⁷

IPv6 /27 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

netmixhosthosthosthosthosthost

Network bits (27)Split hextetHost bits (101)

Network bits: 27
Host bits: 101
Prefix mask: ffff:ffe0::
Total addresses: 2¹⁰¹
Approx. count: 2.54 × 10³⁰
/64 subnets: 2³⁷
Addresses formula: 2^101
/64 relationship: 2³⁷ × /64 subnets

Overview

Common use cases

Aggregating ISP /32 allocations in routing tables
Regional provider address planning
Large-scale subnetting study and documentation

Key facts

A /27 fixes 27 network bits and leaves 101 host bits — 2¹⁰¹ total addresses.
In network design terms, /27 is typically a large provider aggregation block.
You can subnet a /27 into about 2³⁷ /64 LANs.
At site scale, /27 equals about 2²¹ /48 allocations.
At ISP scale, /27 contains 2⁵ /32 blocks.

Design guidance

A /27 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 /27 (or larger) upstream keeps global routing tables manageable.

Practical example

An ISP holding 2001:db8::/27 might announce the entire /27 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 /27 into…

Prefix	Subnets	Addresses each
/28	2	2¹⁰⁰
/29	4	2⁹⁹
/31	16	2⁹⁷
/35	256	2⁹³

/27 fits inside…

Supernet	Addresses	/27s inside
/26	2¹⁰²	2
/25	2¹⁰³	4
/23	2¹⁰⁵	16
/19	2¹⁰⁹	256

Notable /27 networks

2001:db8::/32Documentation prefix (RFC 3849)

Frequently asked questions

Common questions about IPv6 /27 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