IPv6 /32 Prefix ReferenceIPv6
Where ISPs begin: a /32 is the typical entry-level IPv6 allocation an RIR hands a new operator, and it contains 4,294,967,296 /64 subnets. The very first of those subnets already outnumbers the entire IPv4 Internet.
/32 facts at a glance
- Total addresses
- 79,228,162,514,264,337,593,543,950,336 (296)
- /64 subnets inside
- 4,294,967,296
- Host/interface bits
- 96
- Example network
- 2001:db8::/32
- First address
- 2001:db8::
- Last address
- 2001:db8:ffff:ffff:ffff:ffff:ffff:ffff
- Typical role
- ISP or large-enterprise allocation
A /32 in documentation space
Using 2001:db8::/32 (RFC 3849 documentation space) aligned to its own boundary, a /32 occupies:
| Block | First address | Last address |
|---|---|---|
| 2001:db8::/32 | 2001:db8:: | 2001:db8:ffff:ffff:ffff:ffff:ffff:ffff |
How an IPv6 /32 prefix works
A /32 prefix pins the first 32 bits of a 128-bit address, leaving 96 bits free. That free portion holds 296 = 79,228,162,514,264,337,593,543,950,336 distinct addresses, and every such block begins at a multiple of that size. Because each subnet should be a /64, the 32 middle bits between the prefix and the /64 boundary give 4,294,967,296 subnets to hand out.
Where /32 is used
- Startup allocations to ISPs and LIRs from regional registries.
- Large hosting platforms carving per-customer blocks out of one aggregate.
- A single clean BGP announcement that is subdivided only downstream.
Registries size these blocks for decades of growth. Announce the /32 whole at your border and delegate smaller pieces (a /48 here, a /56 there) as customers attach.
Frequently asked questions
How many /64s are in a /32?
4,294,967,296. The difference between the prefixes is sixteen bits, and two raised to the sixteenth power gives just over four billion standard subnets.
Why do ISPs get a whole /32?
RIR policies treat /32 as the typical minimum allocation for operators, sized generously because IPv6 was designed so that scarcity never repeats the IPv4 story.
Isn't handing out billions of subnets wasteful?
No by design. With 128 bits total, liberal allocation costs nothing operationally, and hierarchical aggregation keeps global routing tables small.
Open this prefix in the calculator
Open 2001:db8::/32 in the IPv6 calculator