IPv6 /36 Prefix ReferenceIPv6
The quiet middleweight of IPv6 planning: a /36 packs 268,435,456 /64 subnets into a block that reads cleanly in hexadecimal and splits on every convenient boundary. Too small for an ISP's opening hand yet far bigger than one building — it belongs to large campuses and platform builders.
/36 facts at a glance
- Total addresses
- 4,951,760,157,141,521,099,596,496,896 (292)
- /64 subnets inside
- 268,435,456
- Host/interface bits
- 92
- Example network
- 2001:db8::/36
- First address
- 2001:db8::
- Last address
- 2001:db8:fff:ffff:ffff:ffff:ffff:ffff
- Typical role
- Mid-size ISP allocation
A /36 in documentation space
Using 2001:db8::/32 (RFC 3849 documentation space) aligned to its own boundary, a /36 occupies:
| Block | First address | Last address |
|---|---|---|
| 2001:db8::/36 | 2001:db8:: | 2001:db8:fff:ffff:ffff:ffff:ffff:ffff |
How an IPv6 /36 prefix works
A /36 prefix pins the first 36 bits of a 128-bit address, leaving 92 bits free. That free portion holds 292 = 4,951,760,157,141,521,099,596,496,896 distinct addresses, and every such block begins at a multiple of that size. Because each subnet should be a /64, the 28 middle bits between the prefix and the /64 boundary give 268,435,456 subnets to hand out.
Where /36 is used
- Large enterprise campuses that want room to route hundreds of segments.
- Hosting and cloud platforms subdividing the block into tidy /40s or /44s.
- Mid-tier operators growing toward a fuller /32 over time.
Every split is clean: a /36 yields sixteen /40s, 256 /44s, or 4,096 /48s — all nibble-friendly sizes for reverse DNS.
Position matters in the ladder: sixteen /36s tile a /32, and sixteen /40s tile a /36 — a neat geometric progression for planners.
Frequently asked questions
How many /40s are in a /36?
Sixteen. Four bits of difference, so the /36 divides evenly into 16 blocks of /40.
How many addresses does a /36 contain?
4,951,760,157,141,521,099,596,496,896 — which is 2^92, all inside a prefix that still fits on one clean BGP announcement.
Is a /36 bigger than a /48?
Considerably: 4,096 times bigger, since twelve bits separate them. A /36 holds 4,096 classic site allocations.
Would an ISP hand me a /36?
Unusual as a formal allocation, but perfectly normal as an internally carved slice of a larger grant or a special arrangement for a heavyweight customer.
Open this prefix in the calculator
Open 2001:db8::/36 in the IPv6 calculator