Split an IPv6 address into its network prefix and 64-bit interface identifier, with the identifier type flagged.
Splitting at the prefix boundary separates the routed portion from the host portion. Addresses built by SLAAC from a MAC keep the ff:fe signature; RFC 4941 privacy addresses and static assignments do not. An interface identifier that encodes a MAC address leaks hardware vendor and tracks a device across networks, which is exactly what privacy extensions exist to prevent.
IPv6 Interface ID
The interface identifier is the low 128 − prefix bits; an EUI-64 identifier carries the fixed ff:fe pattern in the middle.
The interface identifier is the low 128 − prefix bits; an EUI-64 identifier carries the fixed ff:fe pattern in the middle. Splitting at the prefix boundary separates the routed portion from the host portion. Addresses built by SLAAC from a MAC keep the ff:fe signature; RFC 4941 privacy addresses and static assignments do not.
An interface identifier that encodes a MAC address leaks hardware vendor and tracks a device across networks, which is exactly what privacy extensions exist to prevent.
This calculator takes 2 inputs: IPv6 address, Prefix length. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.