More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /7 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 /7
- Prefix mask: fe00::
- Total addresses: 2¹²¹
- Approx. count: 2.66 × 10³⁶
- /64 subnets: 2⁵⁷
IPv6 /7 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
- Network bits
- 7
- Host bits
- 121
- Prefix mask
- fe00::
- Total addresses
- 2¹²¹
- Approx. count
- 2.66 × 10³⁶
- /64 subnets
- 2⁵⁷
- Addresses formula
- 2^121
- /64 relationship
- 2⁵⁷ × /64 subnets
Overview
A /7 defines the Unique Local Address (ULA) range fc00::/7 — the IPv6 equivalent of RFC 1918 private space. Addresses here are used inside an organization and are not globally routable on the public internet. The commonly used subset is fd00::/8.
Common use cases
- Private internal networks (ULA)
- Lab and data-center networks isolated from the internet
- VPN and overlay networks with local-only addressing
Key facts
- A /7 fixes 7 network bits and leaves 121 host bits — 2¹²¹ total addresses.
- In network design terms, /7 is typically a IANA reserved / special-purpose block.
- You can subnet a /7 into about 2⁵⁷ /64 LANs.
- At site scale, /7 equals about 2⁴¹ /48 allocations.
- At ISP scale, /7 contains about 2²⁵ /32 blocks.
Design guidance
A /7 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::/7 fall in reserved or special-purpose space. They illustrate how a /7 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)
- RFC 4193Unique Local IPv6 Unicast Addresses (ULA)
Prefix sizing reference
Notable /7 networks
fc00::/7Unique Local Addresses (ULA)fd00::/8Locally assigned ULA (most common)2001:db8::/32Documentation prefix (RFC 3849)
Frequently asked questions
Common questions about IPv6 /7 blocks, prefix sizes, and use cases.