Microsoft IPv6 address vs IPv6 EUI-64 adress plus what is that % mean?

Working through my cisco certification you learn about EUI-64. Essentially it takes your make address and converts it into an IPv6 address. Let’s look at an example:

• MAC: 0000.1111.1111.1111
• IPv6 EUI-64 Link Local Address – FE80::0200:111FF:FE1:1111

Let’s look at a couple of things first. You might notice a “0” turned into a “2” and “FFFE” was thrown in the middle.

The “7th” bit always get’s inverted when making a EUI-64 address. Let’s look at the bits and see how “2” was made. Below is the binary representation of the first 16 bits of Local Identifier.

In hex each character has a potential value from 0->15. That means Each character can be represented in binary by 4 bits. Let’s break down “0000” into 4 separate sections. I will make the 7th bit red and underlined.

0000 0000 0000 0000

Let’s “flip” the bit. To flip the bit “0” becomes a “1” and a “1” becomes a “0”.

0000 0010 0000 0000

the character equals “0010” in binary which is equal to:

(8×0)+(4×0)+(2×1)+(1X0) = 2

Because of this the conversion then looks like “0200”

Next because we need a host ID that is 64bits they take the 48bit Mac address and add 16 more bits and “pad the middle” of the address with “FFFE”.

You might be wondering why I am mentioning all this! Microsoft saw early on that people and computers could be easily tracked by companies if their addresses were made up of their never changing “Burned-in” Mac addresses!

Because of this RFC 3041 was made. It was made to create a random generated Host-ID so that companies like Google couldn’t easily track you.

Click the picture to see it blown up. Notice how the MAC address isn’t inside the Link-Local IPv6 Address!

Here’s a link from Microsoft. The randomly generated info is near the bottom: http://msdn.microsoft.com/en-us/library/aa915616.aspx

Notes on EUI-64:

http://howdoesinternetwork.com/2013/slaac-ipv6-stateless-address-autoconfiguration

So what is up with the % and then number in Microsoft’s IPv6 addresses. In IP 4 what would happen if you had an IP address on separate NIC’s that were in the same network?

eg: NIC #1 – 10.1.1.1 /24 and NIC #2 set to 10.1.1.2 /24?

Wouldn’t work right?

Well the % serves as a zone identifier! http://superuser.com/questions/99746/why-is-there-a-percent-sign-in-the-ipv6-address