More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /30 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 /30
- Prefix mask: ffff:fffc::
- Total addresses: 2⁹⁸
- Approx. count: 3.17 × 10²⁹
- /64 subnets: 2³⁴
IPv6 /30 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
- Network bits
- 30
- Host bits
- 98
- Prefix mask
- ffff:fffc::
- Total addresses
- 2⁹⁸
- Approx. count
- 3.17 × 10²⁹
- /64 subnets
- 2³⁴
- Addresses formula
- 2^98
- /64 relationship
- 2³⁴ × /64 subnets
Overview
A /30 block fixes the first 30 bits of the address, leaving 98 host bits and 2⁹⁸ total addresses. It subdivides into about 2³⁴ /64 LAN subnets. That is also 2¹⁸ /48 site allocations. At the ISP tier, a /30 holds 2² /32 ISP blocks. Prefixes in this range appear in BGP tables and RIR allocation policies as aggregation blocks above the standard ISP /32.
Common use cases
- Aggregating ISP /32 allocations in routing tables
- Regional provider address planning
- Large-scale subnetting study and documentation
Key facts
- A /30 fixes 30 network bits and leaves 98 host bits — 2⁹⁸ total addresses.
- In network design terms, /30 is typically a large provider aggregation block.
- You can subnet a /30 into about 2³⁴ /64 LANs.
- At site scale, /30 equals 2¹⁸ /48 allocations.
- At ISP scale, /30 contains 2² /32 blocks.
Design guidance
A /30 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 /30 (or larger) upstream keeps global routing tables manageable.
Practical example
An ISP holding 2001:db8::/30 might announce the entire /30 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 /30 networks
2001:db8::/32Documentation prefix (RFC 3849)
Frequently asked questions
Common questions about IPv6 /30 blocks, prefix sizes, and use cases.