More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /109 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 /109
- Prefix mask: ffff:ffff:ffff:ffff:ffff:ffff:fff8:0
- Total addresses: 2¹⁹
- Approx. count: 5.24 × 10⁵
- /64 subnets: —
IPv6 /109 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
netnetnetnetnetnetmixhost
Network bits (109)Split hextetHost bits (19)
- Network bits
- 109
- Host bits
- 19
- Prefix mask
- ffff:ffff:ffff:ffff:ffff:ffff:fff8:0
- Total addresses
- 2¹⁹
- Approx. count
- 5.24 × 10⁵
- /64 subnets
- —
- Addresses formula
- 2^19
- /64 relationship
- smaller than a /64
Overview
A /109 provides 2¹⁹ addresses — a tightly scoped segment much smaller than a /64. It is occasionally used for management networks or lab exercises where a full /64 is unnecessary.
Common use cases
- Constrained management or out-of-band segments
- Lab networks with a fixed address budget
- Documentation of smaller-than-/64 designs
Key facts
- A /109 fixes 109 network bits and leaves 19 host bits — 2¹⁹ total addresses.
- In network design terms, /109 is typically a constrained management or lab segment.
- Written out, /109 holds exactly 524,288 addresses.
- A /109 is 1/2⁴⁵ of a standard /64 LAN subnet.
Design guidance
A /109 can work for small management VLANs, out-of-band networks, or certification lab exercises where you deliberately cap the host count. For router interconnects, prefer /127 (RFC 6164) over /109. For ordinary LANs, stay with /64 regardless of how small the segment feels.
Practical example
In a lab, 2001:db8:abcd:0012::1/109 might number a small segment with 524,288 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 /109 blocks, prefix sizes, and use cases.