MAC to IPv6 (EUI-64) Converter

About MAC to IP Converter

There is no formula from a MAC address to an IPv4 address. The two belong to different layers: the MAC is burned into the network card, and the IP address is handed out by whatever network it joins — the same laptop gets a different one at home, at work and in a café. The only thing that connects them is a table each machine keeps of who answered for which address: ARP for IPv4, the neighbour cache for IPv6. So that direction is answered by reading such a table. Paste the output of arp -a, ip neigh or a switch's show ip arp, and the IP addresses recorded for the MAC are listed.

IPv6 is different, because a device can build its address from its MAC. SLAAC takes the 48-bit MAC, puts FF:FE in the middle and flips the universal/local bit to get a 64-bit interface identifier — modified EUI-64, from RFC 4291 — and appends that to the network's /64 prefix. This computes it: for the link-local prefix fe80::/64 that every IPv6 interface has, or for any /64 you give it.

It works backwards too. An IPv6 address whose interface identifier has FF:FE in the middle was built from a MAC, and the MAC is recovered from it. One without was not — most systems now use random or stable privacy identifiers (RFC 4941, RFC 7217) exactly so their address does not reveal their hardware — and it says so rather than inventing an answer.

Everything is worked out in this browser. The table you paste and the addresses you enter are not sent anywhere.

Where it helps

• Computes the SLAAC address for any /64, and the link-local one every interface has.
• Recovers the MAC from an EUI-64 IPv6 address, and says plainly when an address has no MAC in it.
• Reads macOS, Windows and Linux ARP tables, ip neigh, and Cisco show ip arp output as pasted.
• Lists every entry when no MAC is given, so a table can be read at a glance.
• Runs entirely in the browser: no table or address leaves the page.

Limits

• It cannot invent an IPv4 address from a MAC: that needs the network's ARP table, from a machine on the same segment.
• A device using privacy addresses will not use the EUI-64 address computed here, even on the right network.
• An ARP table only lists devices that talked to that machine recently. Ping the device first if it is missing.
• Routers replace the MAC at every hop, so a table only knows the devices on its own local network.

Frequently asked questions

Can I convert a MAC address to an IP address?

Not by calculation for IPv4: the IP address is assigned by the network, not derived from the hardware. Look the MAC up in an ARP table on the same network (arp -a on Windows and macOS, ip neigh on Linux, or your router's DHCP client list). For IPv6, a device using SLAAC with EUI-64 does form its address from its MAC, and that can be computed.

How is an IPv6 address made from a MAC address?

With modified EUI-64. Split the MAC in half, insert FF:FE between the halves, and flip the seventh bit of the first byte (00 becomes 02). The 64-bit result is the interface identifier, which goes after the network's /64 prefix: 00:1B:63:84:45:E6 under fe80::/64 is fe80::21b:63ff:fe84:45e6.

Why does my device's IPv6 address not match the one calculated here?

Because it uses privacy addresses. Windows, macOS, iOS, Android and most Linux distributions now generate a random temporary identifier (RFC 4941) or a stable private one (RFC 7217) instead of using the MAC, so the address cannot be used to identify the hardware.

How do I find the IP address of a device when I only know its MAC?

From a machine on the same network, ping the broadcast address or scan the subnet so every device answers, then run arp -a (or ip neigh) and paste the output here with the MAC. Your router's list of DHCP clients shows the same pairing.

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