More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /28 subnets
- Expanded address
- Compressed address
- Network (expanded)
- Last address (expanded)
- Prefix mask
- Total addresses (exact)
- Reverse DNS (PTR)
- Host bits / network bits
Hextet breakdown
Quick facts for IPv6 /28
- Prefix mask: ffff:fff0::
- Total addresses: 2¹⁰⁰
- Approx. count: 1.27 × 10³⁰
- /64 subnets: 2³⁶
IPv6 /28 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
- Network bits
- 28
- Host bits
- 100
- Prefix mask
- ffff:fff0::
- Total addresses
- 2¹⁰⁰
- Approx. count
- 1.27 × 10³⁰
- /64 subnets
- 2³⁶
- Addresses formula
- 2^100
- /64 relationship
- 2³⁶ × /64 subnets
Overview
A /28 holds 2¹⁰⁰ addresses — 16 times larger than a /32 ISP allocation. It is used to aggregate a handful of /32 blocks under one routing announcement or to document intermediate tiers in the IPv6 allocation hierarchy between a /32 and a /24.
Common use cases
- Aggregating multiple /32 ISP blocks
- Regional provider address planning
- CCNA / Network+ IPv6 subnetting study
Key facts
- A /28 fixes 28 network bits and leaves 100 host bits — 2¹⁰⁰ total addresses.
- In network design terms, /28 is typically a large provider aggregation block.
- You can subnet a /28 into about 2³⁶ /64 LANs.
- At site scale, /28 equals 2²⁰ /48 allocations.
- At ISP scale, /28 contains 2⁴ /32 blocks.
Design guidance
A /28 belongs in BGP aggregation and RIR allocation planning — not on a VLAN interface. If you are subnetting for a real deployment, work downward: carve /48 or /56 site blocks first, then assign one /64 per LAN. Announcing a single aggregated /28 (or larger) upstream keeps global routing tables manageable.
Practical example
An ISP holding 2001:db8::/28 might announce the entire /28 to upstream providers as one BGP route, then delegate /48 blocks such as 2001:db8:0001::/48 and 2001:db8:0002::/48 to business customers. Each customer subnets their /48 into /64 LANs.
Related RFCs and standards
- RFC 4291IPv6 Addressing Architecture
- RFC 3849IPv6 Documentation Address Prefix (2001:db8::/32)
Prefix sizing reference
Notable /28 networks
2001:db8::/32Documentation prefix (RFC 3849)
Frequently asked questions
Common questions about IPv6 /28 blocks, prefix sizes, and use cases.