OS X started using the privacy address starting in 10.7 Lion, so that's why you see two IPv6 addresses on the TCP/IP tab. Over time, that practice raised concerns about privacy, and so the concept of a second, parallel 'privacy address' or 'temporary address' has developed. What's interesting about EUI-64 is that, in an (ironic) effort to avoid address duplication, the device's hardware MAC address is encoded into the EUI-64 address. To indicate that, you'll see a '/64' appended to the end of the address. The first 64-bits are the address of a specific network, and the next 64-bits are for use inside the network. EUI stands for Extended Unique Identifier. For some time now, OS X and its sibling iOS have used what's called the EUI-64 address. There is a protocol for self-assignment, and it has continued to evolve. (That's a simplification, actually, because the IPv6 address space is segmented for different uses, just like IPv4, but you get the idea.) A device can get away with self-assigning its own IPv6 address because of the vast, and I mean vast, number of IPv6 addresses available: 2 128 = 3.4 x 10 38.įor example, one could assign every square centimeter on the surface of Earth a million different IPv6 addresses each and every second for the next million years and still not exhaust the full 2 128 bit address space. It might be self-assigned or it might be assigned to the device. What's behind this is that the way a device gets its IPv6 address can vary. However, if you dig a little deeper, System Preferences -> Network -> Advanced -> TCP/IP, you'll see two IPv6 addresses. If your Mac detects that your ISP and router are offering IPv6 service, (through a router notification called an 'advertisement,') you'll see a single address there. The most natural thing to do is look at System Preferences -> Network.

Note that, for the sake of privacy, I have obscured part of my own IPv6 addresses. In addition, here is some basic background that may be helpful, ' A Layman's Guide to the IPv6 Transition.'įirst, let's look at what's happening on the Mac. This article assumes you have some basic familiarity with IPv6, namely the way IPv6 addresses are constructed. The goal is to help you interpret what you may see. IPv6 development by the ISPs is moving along at a good pace, and the chances are good now that, soon, you'll encounter an IPv6 address on one of your Apple products. While OS X, with access to the command line and more disclosure in the Network System Preferences, almost nails the details, it's less straightforward with an iPad (or iPhone). But there are a few technical wrinkles to be aware of.

Finding the IPv6 address of your Mac or iPad isn't extremely difficult.

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