IPv6 /29 Prefix ReferenceIPv6
Eight operator blocks under one flag: a /29 spans 2^99 addresses — 633,825,300,114,114,700,748,351,602,688 of them — and divides into exactly eight whole /32s. Prefixes this short live above the level of a single ISP grant, marking the super-aggregates of the largest networks.
/29 facts at a glance
- Total addresses
- 633,825,300,114,114,700,748,351,602,688 (299)
- /64 subnets inside
- 34,359,738,368
- Host/interface bits
- 99
- Example network
- 2001:db8::/29
- First address
- 2001:db8::
- Last address
- 2001:dbf:ffff:ffff:ffff:ffff:ffff:ffff
- Typical role
- Large enterprise block (split from a /28-class allocation)
A /29 in documentation space
Using 2001:db8::/32 (RFC 3849 documentation space) aligned to its own boundary, a /29 occupies:
| Block | First address | Last address |
|---|---|---|
| 2001:db8::/29 | 2001:db8:: | 2001:dbf:ffff:ffff:ffff:ffff:ffff:ffff |
How an IPv6 /29 prefix works
A /29 prefix pins the first 29 bits of a 128-bit address, leaving 99 bits free. That free portion holds 299 = 633,825,300,114,114,700,748,351,602,688 distinct addresses, and every such block begins at a multiple of that size. Because each subnet should be a /64, the 35 middle bits between the prefix and the /64 boundary give 34,359,738,368 subnets to hand out.
Where /29 is used
- Announcing eight startup /32 allocations as one tidy BGP aggregate.
- Backbone operators whose addressing plans outgrow a single standard block.
- Special registry grants made to organizations with exceptional, documented scale.
The math is clean: a /29 equals two /30s, four /31s, or eight /32s. Registries part with blocks shorter than /32 sparingly, typically only after sustained, demonstrated utilization.
Cross-family caution: an IPv4 /29 carries 8 addresses, while its IPv6 namesake carries 2^99.
Frequently asked questions
How many /64s are in a /29?
34,359,738,368. Thirty-five delegation bits separate the prefixes, and 2^35 lands at just under 34.4 billion standard subnets.
How many /32s fit in a /29?
Exactly eight. Three bits of difference means each step from /32 down to /29 doubles the count: 2, 4, 8.
Is an IPv6 /29 the same thing as an IPv4 /29?
Only the number matches. An IPv4 /29 holds 8 addresses; an IPv6 /29 holds 2^99 — an aggregate spanning eight entire ISP allocations.
Can I request a /29 from an RIR?
Possibly, but expect scrutiny: registries typically reserve blocks shorter than /32 for operators that document utilization far beyond an ordinary first allocation.
Open this prefix in the calculator
Open 2001:db8::/29 in the IPv6 calculator