Is a /9 used for normal network assignments?

No. A /9 is astronomically large and falls in reserved or special-purpose space. Practical assignments for sites are /48 or /56; for LANs, /64.

What is the difference between /9 and /10?

A /9 is twice as large as /10. /9 has 2¹¹⁹ addresses; /10 has 2¹¹⁸. Each step down the prefix number doubles the address count.

How does /9 compare to /8?

A /8 is twice as large as /9. Moving from /9 to /8 adds one more fixed network bit, halving the host portion from 2¹¹⁹ to 2¹²⁰ addresses.

How do I calculate an IPv6 /9 subnet?

Enter an IPv6 address and select prefix /9 in the calculator above — or paste full CIDR notation like 2001::/9. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹¹⁹ addresses.

IPv6 /9 Subnet Calculator

Results update as you type

A /9 is a very large reserved-range size — 2¹¹⁹ addresses. It sits between link-local (fe80::/10) and larger IANA allocations. Prefixes this large are documented for address-space planning, not assigned to individual networks.

Prefix length

/128

/9 = 2¹¹⁹ addresses (≈ 6.65 × 10³⁵)

Results for 2000::/9

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 /9

Total addresses≈ 6.65 × 10³⁵ addresses

Address typeGlobally routable scope

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

Neighboring /9 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 /9

Prefix mask: ff80::
Total addresses: 2¹¹⁹
Approx. count: 6.65 × 10³⁵
/64 subnets: 2⁵⁵

IPv6 /9 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

mixhosthosthosthosthosthosthost

Network bits (9)Split hextetHost bits (119)

Network bits: 9
Host bits: 119
Prefix mask: ff80::
Total addresses: 2¹¹⁹
Approx. count: 6.65 × 10³⁵
/64 subnets: 2⁵⁵
Addresses formula: 2^119
/64 relationship: 2⁵⁵ × /64 subnets

Overview

Common use cases

Reserved-range documentation
Address-space planning study
IPv6 certification exercises

Key facts

A /9 fixes 9 network bits and leaves 119 host bits — 2¹¹⁹ total addresses.
In network design terms, /9 is typically a IANA reserved / special-purpose block.
You can subnet a /9 into about 2⁵⁵ /64 LANs.
At site scale, /9 equals about 2³⁹ /48 allocations.
At ISP scale, /9 contains about 2²³ /32 blocks.

Design guidance

A /9 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::/9 fall in reserved or special-purpose space. They illustrate how a /9 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 /9 into…

Prefix	Subnets	Addresses each
/10	2	2¹¹⁸
/11	4	2¹¹⁷
/13	16	2¹¹⁵
/17	256	2¹¹¹

/9 fits inside…

Supernet	Addresses	/9s inside
/8	2¹²⁰	2
/7	2¹²¹	4
/5	2¹²³	16
/1	2¹²⁷	256

Notable /9 networks

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

Frequently asked questions

Common questions about IPv6 /9 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