More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown
Neighboring /49 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 /49
- Prefix mask: ffff:ffff:ffff:8000::
- Total addresses: 2⁷⁹
- Approx. count: 6.04 × 10²³
- /64 subnets: 2¹⁵
IPv6 /49 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ
Network / host bit split
- Network bits
- 49
- Host bits
- 79
- Prefix mask
- ffff:ffff:ffff:8000::
- Total addresses
- 2⁷⁹
- Approx. count
- 6.04 × 10²³
- /64 subnets
- 2¹⁵
- Addresses formula
- 2^79
- /64 relationship
- 2¹⁵ × /64 subnets
Overview
A /49 block fixes the first 49 bits of the address, leaving 79 host bits and 2⁷⁹ total addresses. It subdivides into 2¹⁵ /64 LAN subnets. A /49 is a site or subscriber delegation size — larger than a single /64 LAN but smaller than the classic /48 site block.
Common use cases
- Business site or campus delegation
- ISP customer prefix assignment
- Subdividing into /64 VLANs and LANs
Key facts
- A /49 fixes 49 network bits and leaves 79 host bits — 2⁷⁹ total addresses.
- In network design terms, /49 is typically a medium site or business delegation.
- You can subnet a /49 into 2¹⁵ /64 LANs.
Design guidance
A /49 is a practical site or campus delegation. Give each VLAN, Wi-Fi SSID, and security zone its own /64 — do not subnet below /64 on production LANs. With 2¹⁵ available /64s, you have ample room for guest networks, IoT, management, and lab segments.
Practical example
Suppose your ISP delegates 2001:db8:abcd:1200::/49 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 2¹⁵ 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 /49 blocks, prefix sizes, and use cases.