More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /73 subnets
- Expanded address
- Compressed address
- Network (expanded)
- Last address (expanded)
- Prefix mask
- Total addresses (exact)
- Reverse DNS (PTR)
- Host bits / network bits
Hextet breakdown
20010db8abcd00120000000000000001
NetworkSplit groupHost
Quick facts for IPv6 /73
- Prefix mask: ffff:ffff:ffff:ffff:ff80::
- Total addresses: 2⁵⁵
- Approx. count: 3.60 × 10¹⁶
- /64 subnets: —
IPv6 /73 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
netnetnetnetmixhosthosthost
Network bits (73)Split hextetHost bits (55)
- Network bits
- 73
- Host bits
- 55
- Prefix mask
- ffff:ffff:ffff:ffff:ff80::
- Total addresses
- 2⁵⁵
- Approx. count
- 3.60 × 10¹⁶
- /64 subnets
- —
- Addresses formula
- 2^55
- /64 relationship
- smaller than a /64
Overview
A /73 leaves 55 host bits (2⁵⁵ addresses). It is smaller than a /64 LAN and appears in specialized schemes — for example /96 embeds a 32-bit IPv4 address for NAT64 or IPv4-mapped addressing.
Common use cases
- NAT64 and IPv4-embedded addressing study
- Specialized translation gateway design
- Protocol documentation and examples
Key facts
- A /73 fixes 73 network bits and leaves 55 host bits — 2⁵⁵ total addresses.
- In network design terms, /73 is typically a specialized sub-/64 block.
- A /73 is 1/2⁹ of a standard /64 LAN subnet.
Design guidance
A /73 is a specialized size, not a general LAN substitute. Production VLANs should remain /64. Use /73 only when a protocol or design explicitly calls for it — for example /96 in NAT64 translation — or in controlled lab environments.
Practical example
In a lab, 2001:db8:abcd:0012::1/73 might number a small segment with 2⁵⁵ addresses. In production, you would normally expand this to a full /64 unless you have a documented exception.
Prefix sizing reference
Frequently asked questions
Common questions about IPv6 /73 blocks, prefix sizes, and use cases.