More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /63 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 /63
- Prefix mask: ffff:ffff:ffff:fffe::
- Total addresses: 2⁶⁵
- Approx. count: 3.69 × 10¹⁹
- /64 subnets: 2¹
IPv6 /63 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
- Network bits
- 63
- Host bits
- 65
- Prefix mask
- ffff:ffff:ffff:fffe::
- Total addresses
- 2⁶⁵
- Approx. count
- 3.69 × 10¹⁹
- /64 subnets
- 2¹
- Addresses formula
- 2^65
- /64 relationship
- 2¹ × /64 subnets
Overview
A /63 block fixes the first 63 bits of the address, leaving 65 host bits and 2⁶⁵ total addresses. It subdivides into 2¹ /64 LAN subnets. A /63 is a common prefix-delegation size from ISPs to homes and small offices, carved into multiple /64 LANs.
Common use cases
- Residential ISP prefix delegation (DHCPv6-PD)
- Home networks with multiple /64 VLANs
- Small office subnet planning
Key facts
- A /63 fixes 63 network bits and leaves 65 host bits — 2⁶⁵ total addresses.
- In network design terms, /63 is typically a home or small-office prefix delegation.
- You can subnet a /63 into 2¹ /64 LANs.
- Residential ISPs often delegate /56 or /60; /63 would provide 2¹ home LANs.
Design guidance
A /63 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 /63 provides 2¹ /64 LANs — far more than most households need.
Practical example
Suppose your ISP delegates 2001:db8:abcd:0012::/63 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 2¹ 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 /63 blocks, prefix sizes, and use cases.