How does a /2 relate to 2000::/3?

2000::/3 is global unicast — its first three bits are 001. A /2 fixes only the first two bits, so it is four times larger than /3 and includes global unicast plus adjacent reserved space.

What is the difference between /2 and /3?

A /2 is twice as large as /3. /2 has 2¹²⁶ addresses; /3 has 2¹²⁵. Each step down the prefix number doubles the address count.

How does /2 compare to /1?

A /1 is twice as large as /2. Moving from /2 to /1 adds one more fixed network bit, halving the host portion from 2¹²⁶ to 2¹²⁷ addresses.

How do I calculate an IPv6 /2 subnet?

Enter an IPv6 address and select prefix /2 in the calculator above — or paste full CIDR notation like 2000::/2. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹²⁶ addresses.

IPv6 /2 Subnet Calculator

Results update as you type

A /2 spans one quarter of the IPv6 address space — 2¹²⁶ addresses. The current global unicast range (2000::/3) lives inside the first few bits of this space. A /2 is an aggregation size for documentation, not a practical assignment.

Prefix length

/128

/2 = 2¹²⁶ addresses (≈ 8.51 × 10³⁷)

Results for ::/2

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 /2

Total addresses≈ 8.51 × 10³⁷ addresses

Address typeGlobally routable scope

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

Neighboring /2 subnets

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

Hextet breakdown

20000000000000000000000000000000

NetworkSplit groupHost

Quick facts for IPv6 /2

Prefix mask: c000::
Total addresses: 2¹²⁶
Approx. count: 8.51 × 10³⁷
/64 subnets: 2⁶²

IPv6 /2 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

mixhosthosthosthosthosthosthost

Network bits (2)Split hextetHost bits (126)

Network bits: 2
Host bits: 126
Prefix mask: c000::
Total addresses: 2¹²⁶
Approx. count: 8.51 × 10³⁷
/64 subnets: 2⁶²
Addresses formula: 2^126
/64 relationship: 2⁶² × /64 subnets

Overview

Common use cases

Address-space hierarchy documentation
BGP and RIR training scenarios
Understanding where 2000::/3 sits in the full space

Key facts

A /2 fixes 2 network bits and leaves 126 host bits — 2¹²⁶ total addresses.
In network design terms, /2 is typically a global address-space boundary.
You can subnet a /2 into about 2⁶² /64 LANs.
At site scale, /2 equals about 2⁴⁶ /48 allocations.
At ISP scale, /2 contains about 2³⁰ /32 blocks.

Design guidance

A /2 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 2000::/2 fall in reserved or special-purpose space. They illustrate how a /2 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 /2 into…

Prefix	Subnets	Addresses each
/3	2	2¹²⁵
/4	4	2¹²⁴
/6	16	2¹²²
/10	256	2¹¹⁸

/2 fits inside…

Supernet	Addresses	/2s inside
/1	2¹²⁷	2
/0	2¹²⁸	4

Notable /2 networks

2000::/3Global unicast (within this quarter)
2001:db8::/32Documentation prefix (RFC 3849)

Frequently asked questions

Common questions about IPv6 /2 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