More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /56 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 /56
- Prefix mask: ffff:ffff:ffff:ff00::
- Total addresses: 2⁷²
- Approx. count: 4.72 × 10²¹
- /64 subnets: 2⁸
IPv6 /56 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
- Network bits
- 56
- Host bits
- 72
- Prefix mask
- ffff:ffff:ffff:ff00::
- Total addresses
- 2⁷²
- Approx. count
- 4.72 × 10²¹
- /64 subnets
- 2⁸
- Addresses formula
- 2^72
- /64 relationship
- 2⁸ × /64 subnets
Overview
A /56 is the common allocation for homes and small sites. It provides 256 /64 subnets — enough to give every VLAN, guest network, and IoT segment its own /64. Many ISPs delegate a /56 to residential customers via DHCPv6 Prefix Delegation.
Common use cases
- Residential / home network delegation
- Small office with multiple VLANs
- Per-customer ISP prefix delegation
Key facts
- A /56 fixes 56 network bits and leaves 72 host bits — 2⁷² total addresses.
- In network design terms, /56 is typically a home or small-office prefix delegation.
- You can subnet a /56 into 2⁸ /64 LANs.
- Residential ISPs often delegate /56 or /60; /56 would provide 2⁸ home LANs.
Design guidance
A /56 is a common ISP prefix-delegation size for homes and small offices. Configure your edge router to receive the delegated prefix via DHCPv6-PD, then statically route or assign /64 subnets to each internal interface. Even a /56 provides 2⁸ /64 LANs — far more than most households need.
Practical example
Suppose your ISP delegates 2001:db8:abcd:1200::/56 to your edge router. You could assign 2001:db8:abcd:0012::/64 to your main LAN, 2001:db8:abcd:0013::/64 to guest Wi-Fi, and 2001:db8:abcd:0014::/64 to IoT — using only 3 of the 2⁸ available /64 subnets.
Related RFCs and standards
- RFC 4291IPv6 Addressing Architecture
- RFC 6177IPv6 Address Assignment to End Sites
- RFC 3633IPv6 Prefix Options for DHCPv6 Prefix Delegation
Prefix sizing reference
Frequently asked questions
Common questions about IPv6 /56 blocks, prefix sizes, and use cases.