More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /122 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 /122
- Prefix mask: ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffc0
- Total addresses: 2⁶
- Approx. count: 64
- /64 subnets: —
IPv6 /122 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
netnetnetnetnetnetnetmix
Network bits (122)Split hextetHost bits (6)
- Network bits
- 122
- Host bits
- 6
- Prefix mask
- ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffc0
- Total addresses
- 2⁶
- Approx. count
- 64
- /64 subnets
- —
- Addresses formula
- 2^6
- /64 relationship
- smaller than a /64
Overview
A /122 is a very small block with 2⁶ addresses (64) — comparable in spirit to an IPv4 point-to-point subnet. For router links, /127 (RFC 6164) is the modern best practice.
Common use cases
- Very small point-to-point or stub links
- Lab subnetting exercises
- Legacy designs migrating from IPv4 thinking
Key facts
- A /122 fixes 122 network bits and leaves 6 host bits — 2⁶ total addresses.
- In network design terms, /122 is typically a legacy point-to-point size.
- Written out, /122 holds exactly 64 addresses.
- A /122 is 1/2⁵⁸ of a standard /64 LAN subnet.
Design guidance
A /128 is a host route — one specific address. Use it for loopback (::1/128), anycast service endpoints, or static host routes in routing policy. Do not assign a /128 as a LAN prefix.
Practical example
In a lab, 2001:db8:abcd:0012::1/122 might number a small segment with 64 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 /122 blocks, prefix sizes, and use cases.