IPv6 ULAジェネレータ
RFC 4193に従ったランダムIPv6 Unique Local Address (ULA)を生成します — fd00::/8プレフィックスとランダムな40ビットGlobal IDおよび選択した16ビットSubnet IDを含む、/64アドレスおよび/48サイトプレフィックスの両方として。
入力
16ビットサブネット、1～4桁の16進数(0000～ffff)。上部の40ビットGlobal IDは実行するたびにランダムに生成されます。
出力
/64ネットワーク: fd + ランダムGlobal ID + あなたのSubnet ID、ゼロインターフェース識別子付き。
サイトプレフィックス /48 (fd + Global ID) — ここから65,536個のサブネットを自由に割り当てできます。
ガイド
What this tool does
It generates an IPv6 Unique Local Address (ULA) as described by RFC 4193. ULAs are the IPv6 equivalent of private IPv4 ranges like 10.0.0.0/8 or 192.168.0.0/16: routable inside your own network or between sites you control, but never advertised on the public internet. You get back a ready-to-use /64 address and the /48 site prefix it belongs to.
Anatomy of a ULA
A locally-assigned ULA is built from four parts, 128 bits in total:
- Prefix
fd(8 bits). ULAs live infc00::/7. The 8th bit (the "L" bit) is set to 1 for locally-assigned prefixes, which fixes the first byte atfd— so every address this tool produces startsfd00::/8. - Global ID (40 bits). A pseudo-random value that makes your prefix statistically unique, so two networks that merge later almost certainly won't clash. This tool draws 40 fresh random bits for it on every run.
- Subnet ID (16 bits). Your own subnet number within the site — from
0000toffff, giving you 65,536 subnets. This is the one value you control here. - Interface ID (64 bits). Identifies a host on the subnet. The generated address leaves this as zero, so what you get is a
/64network prefix (…::/64) ready for hosts to fill in.
The first 48 bits (fd + Global ID) are the site prefix, shown separately as the /48. Assign yourself one /48 and you can number every subnet in your organisation underneath it.
How to use it
Enter a Subnet ID (1–4 hexadecimal digits — the default 0001 is fine for a first subnet) and click Generate. Each click produces a new random Global ID, so click again for a different prefix. Copy the /48 to record as your site's block, then use /64s beneath it — one per VLAN or segment — by varying the Subnet ID.
About the Global ID and randomness
RFC 4193 §3.2.2 describes deriving the Global ID from a SHA-1 hash of a timestamp and an EUI-64 identifier. That algorithm exists purely to spread assignments evenly; a directly random 40-bit value reaches the same goal, which is why many real-world ULA generators (and this one) simply use randomness. Pick a Global ID once and keep it — it's meant to be stable for the life of your network.
Privacy
Everything is generated in your browser with Math.random(). No address is sent to a server, logged, or stored, and nothing links a generated prefix back to you. Because Math.random() is not a cryptographic source, treat these prefixes as private-network identifiers, not secrets.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/ipv6-ula-generator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"subnetId": "0001"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `ipv6-ula-generator` tool (IPv6 ULA Generator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.