How many addresses are in an IPv6 /17?

An IPv6 /17 contains 2¹¹¹ addresses. The prefix fixes the first 17 bits; the remaining 111 bits identify individual addresses in the block.

How many /64 subnets fit in a /17?

A /17 can be divided into 2⁴⁷ 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 /17?

A /17 contains 2³¹ /48 site allocations. A /48 is the classic size assigned to a business site or campus.

What is the difference between /17 and /18?

A /17 is twice as large as /18. /17 has 2¹¹¹ addresses; /18 has 2¹¹⁰. Each step down the prefix number doubles the address count.

How does /17 compare to /16?

A /16 is twice as large as /17. Moving from /17 to /16 adds one more fixed network bit, halving the host portion from 2¹¹¹ to 2¹¹² addresses.

How do I calculate an IPv6 /17 subnet?

Enter an IPv6 address and select prefix /17 in the calculator above — or paste full CIDR notation like 2001:db8::/17. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹¹¹ addresses.

IPv6 /17 Subnet Calculator

Results update as you type

A /17 block fixes the first 17 bits of the address, leaving 111 host bits and 2¹¹¹ total addresses. It subdivides into about 2⁴⁷ /64 LAN subnets. That is also about 2³¹ /48 site allocations. At the ISP tier, a /17 holds 2¹⁵ /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

/17 = 2¹¹¹ addresses (≈ 2.60 × 10³³)

Results for 2001::/17

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 /17

Total addresses≈ 2.60 × 10³³ addresses

Address typeGlobally routable scope

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

Neighboring /17 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 /17

Prefix mask: ffff:8000::
Total addresses: 2¹¹¹
Approx. count: 2.60 × 10³³
/64 subnets: 2⁴⁷

IPv6 /17 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

netmixhosthosthosthosthosthost

Network bits (17)Split hextetHost bits (111)

Network bits: 17
Host bits: 111
Prefix mask: ffff:8000::
Total addresses: 2¹¹¹
Approx. count: 2.60 × 10³³
/64 subnets: 2⁴⁷
Addresses formula: 2^111
/64 relationship: 2⁴⁷ × /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 /17 fixes 17 network bits and leaves 111 host bits — 2¹¹¹ total addresses.
In network design terms, /17 is typically a RIR-level aggregation block.
You can subnet a /17 into about 2⁴⁷ /64 LANs.
At site scale, /17 equals about 2³¹ /48 allocations.
At ISP scale, /17 contains 2¹⁵ /32 blocks.

Design guidance

A /17 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 /17 (or larger) upstream keeps global routing tables manageable.

Practical example

An ISP holding 2001:db8::/17 might announce the entire /17 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 /17 into…

Prefix	Subnets	Addresses each
/18	2	2¹¹⁰
/19	4	2¹⁰⁹
/21	16	2¹⁰⁷
/25	256	2¹⁰³

/17 fits inside…

Supernet	Addresses	/17s inside
/16	2¹¹²	2
/15	2¹¹³	4
/13	2¹¹⁵	16
/9	2¹¹⁹	256

Notable /17 networks

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

Frequently asked questions

Common questions about IPv6 /17 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