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SLAAC Address Generator

Networking
e.g. 2001:db8:1:1::/64
Colon, dash, or no-separator format
Secret key for opaque IID generation

About This Tool

🌐 SLAAC Address Generator – Automatic IPv6 Address Configuration

IPv6 Stateless Address Autoconfiguration (SLAAC), defined in RFC 4862, is the mechanism that allows network interfaces to automatically assign themselves IPv6 addresses without a DHCP server. By combining a /64 network prefix (received from a router) with a 64-bit Interface Identifier (IID)derived from the device's MAC address, any host can configure a globally routable IPv6 address in seconds. This tool lets you compute, verify, and explore SLAAC addresses offline — ideal for network engineers, students, and security professionals.

How EUI-64 Address Generation Works

The most common SLAAC method uses the EUI-64 algorithm (RFC 4291) to derive the 64-bit IID from a 48-bit MAC address. The three-step process is:

StepOperationExample
1Start with 48-bit MAC address00:1A:2B:3C:4D:5E
2Split at midpoint and insert FF:FE00:1A:2B:FF:FE:3C:4D:5E
3Flip bit 7 (U/L bit) of first octet02:1A:2B:FF:FE:3C:4D:5E
ResultGroup into 16-bit blocks → EUI-64 IID021a:2bff:fe3c:4d5e

The U/L (Universal/Local) bit — bit 6 of the first octet — is XOR'ed with 0x02. This transforms a globally administered MAC address into a locally unique identifier as required by RFC 4291. The final SLAAC address is simply the /64 prefix followed by the EUI-64 IID:

Prefix:  2001:db8:1:1::/64
IID:     021a:2bff:fe3c:4d5e
SLAAC:   2001:db8:1:1:21a:2bff:fe3c:4d5e

Link-Local Addresses and Why They Matter

Before a router even sends a prefix, every IPv6 interface generates a link-local address using the well-known fe80::/10 prefix combined with the same EUI-64 IID. Link-local addresses are used for Neighbor Discovery Protocol (NDP), Router Solicitation/Advertisement exchanges, and local subnet communication. They are never routed beyond a single network segment. This tool always generates both the global unicast SLAAC address and the link-local address for complete visibility.

Privacy Modes: RFC 7217 and RFC 4941

The classic EUI-64 approach embeds your MAC address in every IPv6 address you use — making you trackable across networks. Two RFC-defined alternatives address this privacy concern:

RFC 7217 – Stable Opaque IID
Generates a deterministic but non-predictable IID using a cryptographic hash of the prefix, MAC address, interface index, and a per-host secret key (SHA-256). The address is stable per network— same every time you connect to the same router — but unknown to external observers who don't possess the secret key.
RFC 4941 – Temporary Privacy Extension
Generates a random IID used for outgoing connections alongside the stable address. This temporary address changes periodically (typically every 24 hours on real systems), making long-term tracking very difficult. It is randomly generated fresh each time you click Generate in this tool.

Reverse DNS PTR Records

This tool also computes the ip6.arpa PTR record for each generated address. In IPv6 reverse DNS, the full 32-hex-digit address is written nibble by nibble in reverse order, with each digit separated by a dot, and the suffix .ip6.arpa. appended. For example:

Address: 2001:db8:1:1:21a:2bff:fe3c:4d5e
PTR:     e.5.d.4.c.3.e.f.f.f.b.2.a.1.2.0
         1.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.

Batch Mode for Network Inventories

The Batch Mode tab accepts up to 500 MAC addresses (one per line) and computes all SLAAC addresses under a common /64 prefix simultaneously. Results are displayed in a scrollable table and can be exported as a CSV file — useful for pre-populating DNS records, firewall rules, or network management systems before devices are deployed.

Supported MAC Address Formats

All common MAC address notation styles are accepted and normalised automatically:

Colon-separated

00:1A:2B:3C:4D:5E

Dash-separated

00-1A-2B-3C-4D-5E

No separator

001A2B3C4D5E

Cisco dot

001a.2b3c.4d5e

Validation and Edge Cases

The tool validates all inputs before generating addresses:

  • Prefix must be a valid IPv6 CIDR with exactly a /64 length — SLAAC is only defined for /64 networks.
  • Multicast MACs (LSB of first octet = 1) trigger a warning because EUI-64 conversion of multicast addresses is non-standard.
  • Broadcast MACs (FF:FF:FF:FF:FF:FF) are rejected since they do not represent a unique interface.
  • RFC 7217 key: if left blank, a default value of default is used; for production use, supply a strong random secret.

Common Use Cases

  • Network planning: Pre-compute expected SLAAC addresses for all devices in an office or data centre before deployment to populate DNS records.
  • Security auditing: Verify whether predictable EUI-64-based addresses are exposed, and evaluate the privacy benefit of RFC 7217 or RFC 4941.
  • IPv6 study: Understand the EUI-64 derivation process step by step with the built-in transformation breakdown panel.
  • Troubleshooting: Cross-check the SLAAC address a device should have auto-configured without needing to inspect live traffic.

Frequently Asked Questions

Is the SLAAC Address Generator free?

Yes, SLAAC Address Generator is totally free :)

Can I use the SLAAC Address Generator offline?

Yes, you can install the webapp as PWA.

Is it safe to use SLAAC Address Generator?

Yes, any data related to SLAAC Address Generator only stored in your browser (if storage required). You can simply clear browser cache to clear all the stored data. We do not store any data on server.

What is SLAAC and how does it work?

SLAAC (Stateless Address Autoconfiguration, RFC 4862) allows IPv6 hosts to automatically configure their own IP addresses without a DHCP server. The host combines a /64 network prefix (advertised by the router via Router Advertisement messages) with a 64-bit Interface Identifier (IID) derived from its MAC address using the EUI-64 algorithm to form a complete 128-bit IPv6 address.

How does EUI-64 convert a MAC address to an IPv6 IID?

The EUI-64 process has three steps: (1) Split the 48-bit MAC address at the midpoint into two 3-byte halves. (2) Insert the bytes FF:FE between the two halves, creating a 64-bit value. (3) Flip bit 7 (the Universal/Local bit) of the first octet — XOR with 0x02 — to comply with RFC 4291. For example, MAC 00:1A:2B:3C:4D:5E becomes EUI-64 IID 021a:2bff:fe3c:4d5e.

What is the difference between EUI-64, RFC 7217, and RFC 4941 modes?

EUI-64 (RFC 4291) embeds your MAC address directly into the IPv6 address, making it globally trackable. RFC 7217 Opaque IID generates a stable but non-predictable IID using a cryptographic hash of the prefix, MAC, and a secret key — preventing MAC-based tracking while keeping the address stable per network. RFC 4941 Privacy Extensions generate a random, temporary IID that changes periodically for outgoing connections, providing the strongest privacy.

Why is the /64 prefix length required for SLAAC?

SLAAC is specifically designed for /64 prefixes. The IPv6 address space is divided into a 64-bit network prefix and a 64-bit Interface Identifier. The EUI-64 algorithm produces exactly 64 bits, so it can only fill the IID portion of a /64 prefix. Networks using prefixes longer than /64 (like /65 to /128) cannot use standard SLAAC.

What is a link-local address and how is it generated?

A link-local address (fe80::/10) is an IPv6 address valid only within a single network segment — it cannot be routed across the internet. Every IPv6 interface automatically generates one using the well-known prefix fe80:: combined with the EUI-64 IID from its MAC address, regardless of whether a router prefix is available. It is used for neighbor discovery and router communication.

What is a Reverse DNS PTR record for an IPv6 address?

A Reverse DNS PTR record maps an IP address back to a hostname. For IPv6, the address is written as a sequence of individual nibbles (hex digits) in reverse order, separated by dots, with the suffix '.ip6.arpa.' appended. For example, 2001:db8::1 maps to '1.0.0.0...8.b.d.0.1.0.0.2.ip6.arpa.' This tool generates the PTR record automatically for every computed address.