MicroNugget: How to Use IPv6 EUI-64 Calculation on an IOS Router

In this video, Keith Barker covers link-local addresses and how they're calculated using IPv6's EUI-64 calculation. This video quickly answers what a link local address is, how hexadecimal notation works, IPv6 IP address segmentation, and how a link-local address gets created for every interface running IPv6.

IPv6 creates many opportunities for routing and addressing that were simply impossible with IPv4. One is EUI-64, a pretty simple calculation that starts with a device's 128-bit IP address and ends with a unique local address specific to that device. That link-local address means that the interface has a global address that's reachable from the rest of the internet, but also an address that's reachable only on the local segment. The magic of creating that link-local address is in splitting the 128-bit IP address in half, and doing some hexadecimal magic to it.

Watch and see the math behind what an IOS router is doing when it takes the MAC address (the Layer 2 address) of the interface and converts its 48 bits into a unique 64-bit identifier. And then watch Keith enable an interface and hard code an IP address — last, see the link-local address get created by the IOS router.

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[ChasedWheels]

WoW. a video from 2012. Where have I been all this time? I feel, I was frozen somewhere and coming back to life with all this technology to catch up.

[KeithBarker]

Hi Dejan- thanks for the comments!

Best wishes,

Keith Barker

[KeithBarker]

Great question.

The first 2 hex characters represent 8 bits. If they are all 0, we would have 0000 0000 (representing 2 groups of 4 bits each). If we flip the 7th bit from the left, we would have 0000 0010. In hex, those 8 bits (represented 4 at a time) would be 0 (for the first 4) and 2 for the second set of four. That is why it would change from hex 00 to hex 02. Each group of 4 bits carry the weights of 8 4 2 1 (and the next group of four do the same).


Keith

[Lashan_]

I've watched so many video courses to no avail. My jaw literally dropped open by the simplicity taught in this nugget. CBT Nuggest you're an absolute blessing, thank you Keith Barker. I'm ready to continue learning/training with you guys.

[KeithBarker]

Thanks. We will keep them rolling.

Keith

[KeithBarker]

Thanks Branimir!

@TheTechnify: Each hex character represents 4 bits (one nibble).

Keith

[keithbarker]

Hello Uttam- Great question.

The answer is yes. Unlike IPv4, we can have not only 2 IPv6 addresses on a single interface at the same time (a link local fe80: and a global, like 2005:) but we can also have multiple global addresses, at the same time.

Hope that helps,

Keith

[XSFlanger]

Interestingly modern windows doesn't comply to EUI-64 policy. Microsoft came up to their own "theory" of randomized autoconfiguration. To disable that mess and enable EUI-64, from command line (with admin rights of course) issue "netsh interface ipv6 set global then disable/enable ipv6 stack (from NIC properties box). Also pay attention to %value suffixes after ipv6. It is zone index of local egress interface, so don't get confused if you see %11 after ipv6 :)

[elnini]

Thanks for the video! Defiantly got a better grasp on the concept though this video rather then trying to through a text book.!

[KeithBarker]

Hello Karim- CBT Nuggets has a complete "GNS3" series which focuses on how to build many different topologies in GNS3.

I would recommend you take a look at it.

Thanks,

Keith

[surelb]

I'm starting learn some ipv6 this is m aking more sense now thank you

[Russdog]

Keep em coming Keith. I like the long videos as well. :)

[clintonoshea]

Thanks loads, Keith! That was a great help :)

[TheTechnify]

Just a question. When the flip happens in seven bit 0000 0000. Shouldn't start the Link local at 0020 instead of 200 ? I am confused.

[abulzawabe]

Thanks for the video Keith. I have a question. Does the IETF have a good reason for flipping the 7th bit ? Or is it just to make things in IT more confusing as usual ??

[hassam]

Thanks keith i really enjoy your nugget thanks you again plugin

[karimel-mesbahi]

hello Keith .. How to build this topology on GNS3

[uttambaroi]

Hi Keith,
Great video, one question...
as you said, every IPv6 interface will have one link local address for local connection and might have Global address for the rest of the world...
Does that mean we can have two IPv6 addresses on one interface Keith ?

kinda confused, please help :)

[B.O.E.A.]

Correct me if i'm wrong but how is FFFE a total of 16 bits? My calculation is that one F is 4 bits so three FFF is 12 bits en E is 3 bits so combined that's 15 bits right??

[uttambaroi]

The reason behind is that you can drop the leading 0 in IPv6