How big is an IPv6 /11?

A /11 contains 2¹¹⁷ addresses. Blocks this large are part of the global allocation hierarchy far above what any single organization receives.

What is the difference between /11 and /12?

A /11 is twice as large as /12. /11 has 2¹¹⁷ addresses; /12 has 2¹¹⁶. Each step down the prefix number doubles the address count.

How does /11 compare to /10?

A /10 is twice as large as /11. Moving from /11 to /10 adds one more fixed network bit, halving the host portion from 2¹¹⁷ to 2¹¹⁸ addresses.

How do I calculate an IPv6 /11 subnet?

Enter an IPv6 address and select prefix /11 in the calculator above — or paste full CIDR notation like 2001::/11. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹¹⁷ addresses.

IPv6 /11 Subnet Calculator

Results update as you type

A /11 holds 2¹¹⁷ addresses and sits in the reserved and special-purpose region of the IPv6 space between major IETF allocations. It is relevant for understanding address architecture, not for day-to-day subnet design.

Prefix length

/128

/11 = 2¹¹⁷ addresses (≈ 1.66 × 10³⁵)

Results for 2000::/11

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 /11

Total addresses≈ 1.66 × 10³⁵ addresses

Address typeGlobally routable scope

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

Neighboring /11 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 /11

Prefix mask: ffe0::
Total addresses: 2¹¹⁷
Approx. count: 1.66 × 10³⁵
/64 subnets: 2⁵³

IPv6 /11 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

mixhosthosthosthosthosthosthost

Network bits (11)Split hextetHost bits (117)

Network bits: 11
Host bits: 117
Prefix mask: ffe0::
Total addresses: 2¹¹⁷
Approx. count: 1.66 × 10³⁵
/64 subnets: 2⁵³
Addresses formula: 2^117
/64 relationship: 2⁵³ × /64 subnets

Overview

Common use cases

IPv6 address architecture study
RIR and IETF documentation
Certification exam preparation

Key facts

A /11 fixes 11 network bits and leaves 117 host bits — 2¹¹⁷ total addresses.
In network design terms, /11 is typically a IANA reserved / special-purpose block.
You can subnet a /11 into about 2⁵³ /64 LANs.
At site scale, /11 equals about 2³⁷ /48 allocations.
At ISP scale, /11 contains about 2²¹ /32 blocks.

Design guidance

A /11 is not a size you assign to a LAN or site. Treat it as documentation of how the IPv6 address space is carved at the top of the hierarchy. When studying for certifications, focus on which well-known ranges (2000::/3, fe80::/10, fc00::/7, ff00::/8) live inside or beside this block.

Practical example

Addresses like 2001::/11 fall in reserved or special-purpose space. They illustrate how a /11 boundary groups addresses for routing policy, not how you would number a home LAN.

Related RFCs and standards

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

Prefix sizing reference

Divide /11 into…

Prefix	Subnets	Addresses each
/12	2	2¹¹⁶
/13	4	2¹¹⁵
/15	16	2¹¹³
/19	256	2¹⁰⁹

/11 fits inside…

Supernet	Addresses	/11s inside
/10	2¹¹⁸	2
/9	2¹¹⁹	4
/7	2¹²¹	16
/3	2¹²⁵	256

Notable /11 networks

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

Frequently asked questions

Common questions about IPv6 /11 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