EUI-64 Configuration
Invalid MAC address — must be 12 hex characters
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IPv6 SLAAC & EUI-64 Generator
Use this tool to convert any MAC address into a 64-bit IPv6 Interface Identifier using the EUI-64 process. See every step — the FF:FE insertion and the 7th-bit flip — explained side by side. Essential for CCNA/CCNP study and stateless autoconfiguration (SLAAC) configuration.
EUI-64 Step-by-Step
7th Bit Flip Shown
FF:FE Insertion
Full IPv6 Address Output
Understanding EUI-64 & SLAAC
What is SLAAC?
Stateless Address Autoconfiguration (SLAAC) allows an IPv6 host to generate its own unique IP address without a DHCPv6 server. The device takes its 48-bit MAC address and converts it into a 64-bit Interface Identifier using the EUI-64 method, then combines it with the network prefix advertised by the router.
The Two-Step EUI-64 Process
Step 1 — FF:FE Insertion
A MAC address is split into two 24-bit halves (OUI and NIC-specific bits). The 16-bit hex value FFFE is inserted in the middle, expanding the 48-bit address into a 64-bit Interface Identifier.
Step 2 — Flip the 7th Bit
The 7th bit of the first octet (the U/L bit) is inverted. A MAC starting with 00 becomes 02. This flags the address as locally administered, which is the SLAAC convention.
Worked Example
Input MAC: 00:00:AA:11:22:33
- Split & Insert FF:FE:
0000:AAFF:FE11:2233 - Binary flip: First octet
00→00000000→ flip 7th bit →00000010→02 - Final Interface ID:
0200:aaff:fe11:2233
Step-by-Step Instructions
- 1Input MAC Address: Paste your device MAC (supports
:,-, and Cisco.dot formats). - 2Optional Prefix: Enter your network prefix (e.g.,
2001:db8::orfe80::) to see the complete IPv6 address. - 3Click Generate: The table shows each transformation step — FF:FE insertion, the bit flip, the resulting Interface ID, and the full address.
Cisco Tip: On Cisco IOS, use
ipv6 address <prefix>/64 eui-64 on an interface to have the router auto-generate its address using this exact process.Frequently Asked Questions
Why is FF:FE inserted in the middle?
MAC addresses are 48 bits, but IPv6 Interface Identifiers must be 64 bits. The IEEE reserved FFFE specifically for EUI-64 conversion — inserting it in the middle of the MAC pads it to 64 bits without conflicting with any real OUI.
What is the U/L bit and why is it flipped?
The 7th bit of the OUI is the Universal/Local bit. In a factory-assigned MAC address it is set to 0 (universal). Flipping it to 1 marks the resulting Interface ID as locally administered, which is the standard convention for SLAAC-generated identifiers per RFC 4291.
Can EUI-64 cause privacy issues?
Yes. Because EUI-64 embeds your hardware MAC address, your device can be tracked across different networks. Most modern operating systems now use IPv6 Privacy Extensions (RFC 4941) to generate random Interface IDs instead, making EUI-64 primarily relevant for routers and infrastructure devices rather than end-user machines.
What MAC formats does this tool accept?
The tool accepts all three common formats: colon-separated (00:11:22:33:44:55), hyphen-separated (00-11-22-33-44-55), and Cisco dot-separated (0011.2233.4455). All separators are stripped before processing.
Does SLAAC replace DHCPv6?
Not entirely. SLAAC handles address assignment automatically, but it cannot distribute DNS server addresses on its own (without Router Advertisements using RDNSS options per RFC 8106). In enterprise environments, DHCPv6 is often used alongside SLAAC (stateless DHCPv6) to provide DNS and domain search options while letting devices self-assign their addresses.