More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /6 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 /6
- Prefix mask: fc00::
- Total addresses: 2¹²²
- Approx. count: 5.32 × 10³⁶
- /64 subnets: 2⁵⁸
IPv6 /6 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
- Network bits
- 6
- Host bits
- 122
- Prefix mask
- fc00::
- Total addresses
- 2¹²²
- Approx. count
- 5.32 × 10³⁶
- /64 subnets
- 2⁵⁸
- Addresses formula
- 2^122
- /64 relationship
- 2⁵⁸ × /64 subnets
Overview
A /6 block fixes the first 6 bits of the address, leaving 122 host bits and 2¹²² total addresses. It subdivides into about 2⁵⁸ /64 LAN subnets. That is also about 2⁴² /48 site allocations. At the ISP tier, a /6 holds about 2²⁶ /32 ISP blocks. Blocks this large are used for IANA and RIR-level address planning, not for individual networks.
Common use cases
- IANA and RIR address-space documentation
- Top-level BGP aggregation planning
- IPv6 certification and training exercises
Key facts
- A /6 fixes 6 network bits and leaves 122 host bits — 2¹²² total addresses.
- In network design terms, /6 is typically a IANA reserved / special-purpose block.
- You can subnet a /6 into about 2⁵⁸ /64 LANs.
- At site scale, /6 equals about 2⁴² /48 allocations.
- At ISP scale, /6 contains about 2²⁶ /32 blocks.
Design guidance
A /6 is not a size you assign to a LAN or site. Treat it as documentation of how the IPv6 address space is carved at the top of the hierarchy. When studying for certifications, focus on which well-known ranges (2000::/3, fe80::/10, fc00::/7, ff00::/8) live inside or beside this block.
Practical example
Addresses like 2001::/6 fall in reserved or special-purpose space. They illustrate how a /6 boundary groups addresses for routing policy, not how you would number a home LAN.
Related RFCs and standards
- RFC 4291IPv6 Addressing Architecture
- RFC 3849IPv6 Documentation Address Prefix (2001:db8::/32)
Prefix sizing reference
Notable /6 networks
2001:db8::/32Documentation prefix (RFC 3849)
Frequently asked questions
Common questions about IPv6 /6 blocks, prefix sizes, and use cases.