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(electronic music)

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- In the previous video, I
introduced you to the concept

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of IPv6 and why it was
created in the first place,

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and we did a brief look
at an IPv6 address,

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and we saw that it was
really big, it was 128 bits

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in binary, and we saw that
instead of representing that

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in dotted decimal notation like we do

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with an IPv4 address, IPv6 addresses

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are represented in hexadecimal,

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that every four bits and
binary are represented by

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a single hexadecimal
character that can be anything

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from zero to F, with zero meaning zero

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and F meaning fifteen,

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and then after four
hexadecimal characters,

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we have the colon.

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And those four hexadecimal
characters together

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were called a word.

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Sixteen bits is called a word,

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so for every word there was a colon.

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So now what we're going to look at is,

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normally in discussing IP addresses,

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I would focus on the
network portion first,

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because that's what we did with IPv4,

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and we talked all about
the network portion,

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but in order to really talk
about the network portion

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of an IPv6 address, first we
actually have to understand the

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second half of the
address, the host portion.

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Because the host portion,
you come up with that

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in a slightly different
way than we do in IPv4,

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and I'm going to be using
a term called EUI-64.

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EUI-64 is one of the ways
that the host portion

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of an IPv6 address is created,

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and I'm going to be
referencing that term a lot

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when I'm talking about
various different kinds of

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IPv6 addresses, and if you
didn't know what EUI-64 meant,

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that would be kind of meaningless to you.

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So, let's talk about the host portion.

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So, in the world of routed protocols,

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a routed protocol by
definition has to provide

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some sort of layer three address

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to what is being encapsulated.

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And we know that a routed protocol,

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whatever that address is,
however big or small it is,

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it has to be sub-dividable
into two pieces.

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Part of the address has to be the network,

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or sometimes we call the prefix,

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the other half of the
address is the host ID,

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or sort of like the serial
number of the individual host

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in that network.

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So it has to be sub-dividable
into two pieces.

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So we mentioned, we talked about IPv4,

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we looked at how the
subnet mask was the tool,

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the comparison tool that
we use against the IPv4

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address, to determine where
that dividing line was,

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between the network portion
and the host portion.

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So in an IPv6 address, same rules apply.

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Even though the address is much bigger,

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we need a subnet mask,
and a subnet mask tells us

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where within those 128 bits
the dividing line needs to be.

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Now in IPv6, the second
portion of the address

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that is unique just to your laptop,

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technically those bits, we
don't call them host bits.

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We have a different name for them.

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They're called the interface ID.

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It means basically the same thing,

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your interface ID, your
host bits, same thing.

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It's a unique set of bits just for you

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on this particular network that
you're sitting on right now.

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But you should be familiar
with the fact that we

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no longer call them host bits,

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they're called an interface ID.

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Now, according to the Internet
Assigned Numbers Authority,

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remember them?

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They're at the top of the
food chain as far as governing

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all numbers related to the internet,

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they really strongly advise
that IPv6 addresses be split

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evenly right down the middle.

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That the first 64 bits be for
the prefix, or the network,

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and the second 64 bits
be for the interface ID.

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Now it's a recommendation.

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You don't have to do that.

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Just like in the world of IPv4,

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if I gave you a 32 bit
IP version 4 address,

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you could create whatever
subnet mask you wanted to,

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to put that dividing line
wherever you wanted to.

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You could say that the first
19 bits are the network,

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or the first 26 bits,
or the first 12 bits.

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Same thing is true with IPv6.

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Anywhere within those 128 bits,

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you could set that dividing line,

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but, the problem is, if
you don't go with the

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recommendation of cutting
it right down the middle,

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then some of the other
benefits that you have

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of IPv6 are lost.

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Some of the other benefits
that come with IPv6

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you cannot take advantage of if you don't

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split your address right down the middle.

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So that's why it's just really
a good idea to do what the

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Internet Assigned Numbers
Authority recommends that you do.

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Okay, so the nice thing here,
one thing that's kind of

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easier, okay, yeah, it's kind
of disappointing that when

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we're representing the IPV6
address itself, it's so big,

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and we have to remember all
these hexadecimal characters,

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and where the colons go.

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So yes, an IPv6 address,
typing it into the keyboard

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is a lot more cumbersome than
typing in an IPv4 address.

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But, there is a trade off.

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When you're typing in your IPv4 address,

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when you get to the subnet mask,

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you had to type in the
subnet mask as another

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dotted decimal number,
255.255.255.whatever, 248.

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In IPv6 as you can see here on the slide,

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you can actually type in the subnet mask,

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actually, you don't have a choice.

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You type in the subnet mask
as the shorthand notation,

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as a forward slash and a number,

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like /64 is what you would commonly see.

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So like this number here
that we see in black,

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2001, and then ending with ::3a/64.

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That is exactly how you
would type an IPv6 address

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into your router's interface, for example.

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So when we get to actually
configuring routers

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and switches and putting
addresses on them,

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we'll use the IP address
command to put in IPv4 address,

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and we'll use the IPv6 address command

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to put an IPv6 address.

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And with the v6, we will not
have to use dotted decimals

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for the subnet mask, so
that will be kind of nice.

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Now let's do some comparing
and contrasting here.

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With IPv4, which is what
you're most familiar with

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right now, how does a device,

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let's just think about
a laptop for a moment,

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how can a laptop obtain an IPv4 address?

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How does it get on your system?

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What are the various ways?

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Well, hopefully you said, if
you're talking about Microsoft

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Windows specifically, there
are three ways, right?

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You could get it via DHCP,

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and that is the way the vast
majority of hosts obtain

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their IP addresses,

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via the Dynamic Host
Configuration Protocol,

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on by default.

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Or, if we're talking about
a host that never moves,

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like a server that's
always in one position,

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we could statically
configure it on that device

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so it always has the
exact same IP address,

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or if we're talking
about Microsoft Windows,

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we know that if Windows
is configured to try DHCP,

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and then DHCP fails,

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it will fall back to that 169.254 address,

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that automatically provisioned IP address.

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So those are the three ways,

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and that last one, we don't
really like to see, right?

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When we're on a Windows device,

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and we see that the IP
address is 169, it's like,

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uh-oh, that's not a good
thing, it should not be that.

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Well, in the world of IPv6,

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you have the first two
methods are exactly the same.

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There is a DHCP version
of IP, it's called DHCPv6,

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so you can certainly use that.

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You can still statically
configure your IPv6 address

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on your laptop or on your router,

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or, IPv6 actually has a
totally unique way that IPv4

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doesn't have which is called

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Stateless Address Automatic
Aonfiguration, SLAAC.

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Stateless Address Automatic Configuration.

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And by using SLAAC, an
interface, a nic card,

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can automatically obtain a
globally routable prefix,

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a prefix that actually could be used

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to get to and from the
internet without using DHCP.

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And towards the end of my
IPv6 discussion videos,

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we'll talk a little bit about that,

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when we talk about something
called IPv6 neighbor discovery,

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that is how Stateless Address
Automatic Configuration works.

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But that's something that's
kind of unique to IPv6,

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where it doesn't need
technically DHCP to get

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a useful address for itself.

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Now, I want to focus in here
in this presentation on the

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interface ID, so let me
bring up the whiteboard here,

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and zoom in on this.

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So let's say that I was
on a router and I am at,

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I mentioned this mode briefly,

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do you remember what I called this mode

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in some previous videos?

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This was called User
Exec mode, and I said,

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you really can't do much from this level,

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so I said we want to move
up to the next level,

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which, what does the prompt look like,

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what symbol does it take
at the next higher level?

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It's a pound sign.

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And what did we technically
call this configuration mode,

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or level?

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This was called Privileged
Exec, Privileged Exec.

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Now what actual IOS command
did I have to type in

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when I was at User Exec level to get me to

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Privileged Exec?

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That was the single word of enable,

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and that's why Privileged
Exec is sometimes called

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Enable Mode, you'll hear that a lot,

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but technically it's
called Privileged Exec.

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Okay, now from Privileged Exec mode,

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can I start configuring this device?

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Can I start adding IP addresses,

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and turning on routing
protocols, and doing all of that?

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No, I can't.

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So now I need to get to another mode.

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What is the next mode
called that will actually be

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the very first mode that allows me to do

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any kind of configuration?

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That mode is called
Global Configuration Mode.

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And what would the prompt
look like to tell me

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that I'm in Global Configuration Mode?

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I would see in parentheses
the word config,

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and the the hash symbol.

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And, review question.

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How do I get from Privileged Exec

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into Global Configuration Mode?

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I have to type two words,
configure terminal.

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Most people usually
shorten that to config t.

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Cisco IOS does recognize
that config t means

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configure terminal.

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Okay.

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So right now, let's say
that I have a router

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that looks like this, it's
got two interfaces on it,

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and the interface where
I want to apply my IPv6

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and my IPv4 address,

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I'm going to make this
a dual stack device,

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It's going to run both v4 and v6.

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It's FastEthernet 0/0.

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From right where I am right here,

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can I start configuring my
IPv4 and my IPv6 addresses?

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No, I cannot.

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The router can't guess my mind,

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it doesn't know which interface

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that any address would go
on, so I have to tell it.

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So in this particular case,

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from Global Configuration mode,

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I would say, okay, the
interface I want to go to is

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FastEthernet 0/0, and now that
will put me into yet another

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submode called config interface mode.

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So now, anything I type,
a relevant command,

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it recognizes there's
some commands that are

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appropriate for putting on this interface,

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and there are some commands
that are not appropriate.

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If I tried typing in a
command here for example to

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change the name of the router,

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let's say I said oh, I don't
want it to be called router,

248
00:12:24,974 --> 00:12:27,693
I want to be called Keith's Router.

249
00:12:27,693 --> 00:12:29,677
Well, if I tried typing
in the command to do that

250
00:12:29,677 --> 00:12:32,676
right here, it would
recognize that that command

251
00:12:32,676 --> 00:12:34,971
was not at the appropriate level,

252
00:12:34,971 --> 00:12:37,021
and it would either get
me an error message,

253
00:12:37,021 --> 00:12:38,835
or it would bounce me
back to the level where

254
00:12:38,835 --> 00:12:39,909
I'm supposed to be.

255
00:12:39,909 --> 00:12:44,375
But right now, I want to
type in an IPv4 address.

256
00:12:44,375 --> 00:12:47,041
So let's say I want to give
this thing the IPv4 address

257
00:12:47,041 --> 00:12:50,291
of 20.1.1.1 with a /24 mask.

258
00:12:51,902 --> 00:12:55,902
Do you remember what the
command was to do that?

259
00:12:57,728 --> 00:13:01,895
That command was IP address,
which means it was an

260
00:13:02,795 --> 00:13:06,962
IPv4 address, 20.1.1.1, and
then we have to put in our

261
00:13:08,001 --> 00:13:10,501
subnet mask in dotted decimal.

262
00:13:11,635 --> 00:13:14,398
Okay, and then as soon
as I hit the enter key,

263
00:13:14,398 --> 00:13:16,730
that will take effect,

264
00:13:16,730 --> 00:13:18,766
and it will put me right back

265
00:13:18,766 --> 00:13:21,483
in Interface Configuration Mode.

266
00:13:21,483 --> 00:13:22,477
I haven't left it yet,

267
00:13:22,477 --> 00:13:25,130
it assumes I still want to be there.

268
00:13:25,130 --> 00:13:28,047
Now, let's say, I'm going to
have to use an arrow here,

269
00:13:28,047 --> 00:13:31,297
because an IPv6 address is quite large,

270
00:13:32,158 --> 00:13:35,324
let's say that on that same interface,

271
00:13:35,324 --> 00:13:39,074
I want to apply an IPv6
address that is this.

272
00:13:43,646 --> 00:13:46,313
Let's say it's 2001:1111:0:aaaa,

273
00:13:52,523 --> 00:13:54,694
okay, so right there, if we add that up,

274
00:13:54,694 --> 00:13:56,354
that's the first half of my address,

275
00:13:56,354 --> 00:13:57,482
that's my network,

276
00:13:57,482 --> 00:13:59,002
because remember, this is a word.

277
00:13:59,002 --> 00:14:01,922
2001 is a word, and a word is 16 bits,

278
00:14:01,922 --> 00:14:05,672
so 16 plus 16, plus 16,
plus 16, gives me 64,

279
00:14:08,454 --> 00:14:12,010
so there's my prefix,
I'll put a colon there.

280
00:14:12,010 --> 00:14:15,382
Now the rest of this
address is going to be my

281
00:14:15,382 --> 00:14:18,715
interface ID, and then at the end of it,

282
00:14:19,835 --> 00:14:24,002
I'm going to put /64 to
indicate that this portion

283
00:14:25,567 --> 00:14:26,817
is the network.

284
00:14:27,848 --> 00:14:29,982
Now as far as the
interface ID is concerned,

285
00:14:29,982 --> 00:14:32,993
on the router, I have two choices.

286
00:14:32,993 --> 00:14:35,471
I could statically configure it.

287
00:14:35,471 --> 00:14:37,059
Maybe I want it to be like this,

288
00:14:37,059 --> 00:14:41,226
maybe I want the interface
ID to be 2222:1111:0:a,

289
00:14:44,846 --> 00:14:48,346
well then I would simply type IPv6 address

290
00:14:51,294 --> 00:14:53,294
2001:1111:0:aaaa, colon,

291
00:14:58,881 --> 00:15:02,964
and then I would put 2222:1111:0:a/64.

292
00:15:12,468 --> 00:15:15,635
So by manually typing in this portion,

293
00:15:16,672 --> 00:15:20,175
I've just statically
provided the last 64 bits.

294
00:15:20,175 --> 00:15:23,243
I've told it what its
interface ID should be.

295
00:15:23,243 --> 00:15:25,620
Just like when I gave the IPv4 address,

296
00:15:25,620 --> 00:15:27,948
part of this was the host bits.

297
00:15:27,948 --> 00:15:30,949
I told it what the host bits were.

298
00:15:30,949 --> 00:15:33,331
But with IPv6, there is an alternative.

299
00:15:33,331 --> 00:15:35,778
Now usually when you're
talking about devices

300
00:15:35,778 --> 00:15:38,198
that have static IP addresses,

301
00:15:38,198 --> 00:15:41,491
like routers interfaces, like servers,

302
00:15:41,491 --> 00:15:43,331
you would want to do this,

303
00:15:43,331 --> 00:15:45,851
you would want to give
it a static interface ID,

304
00:15:45,851 --> 00:15:48,127
and probably something
that's easy to remember,

305
00:15:48,127 --> 00:15:52,044
like 000001, or 000002,
or something like that.

306
00:15:53,299 --> 00:15:56,185
This one here is not all
that easy to remember.

307
00:15:56,185 --> 00:15:59,768
But, on laptops and
tablets and smartphones

308
00:16:00,691 --> 00:16:04,858
that are running IPv6,
typically they get all of their

309
00:16:06,283 --> 00:16:08,949
address information dynamically,

310
00:16:08,949 --> 00:16:11,449
and so they will obtain their prefix,

311
00:16:11,449 --> 00:16:13,324
their network dynamically,

312
00:16:13,324 --> 00:16:16,131
and then they will by
themselves come up with

313
00:16:16,131 --> 00:16:20,620
their interface ID without
any help from anybody else.

314
00:16:20,620 --> 00:16:24,708
Now if I wanted the router
to do that same thing,

315
00:16:24,708 --> 00:16:26,670
I could type this.

316
00:16:26,670 --> 00:16:29,170
IPV6 address 2001.1111.0.aaaa,

317
00:16:34,577 --> 00:16:37,744
and then I would say ::/64,

318
00:16:39,390 --> 00:16:41,170
so now remember, what does the :: mean?

319
00:16:41,170 --> 00:16:44,382
That means this covers
a whole bunch of zeros,

320
00:16:44,382 --> 00:16:48,130
so right now I've given him
his first 64 bits and the ::

321
00:16:48,130 --> 00:16:51,924
is saying the last 64 bits are zeros,

322
00:16:51,924 --> 00:16:54,950
but I'm going to add one
additional element here

323
00:16:54,950 --> 00:16:56,612
to tell him, well wait a second,

324
00:16:56,612 --> 00:16:59,280
I don't want your interface
ID to be all zeros,

325
00:16:59,280 --> 00:17:03,447
I want you to make it up yourself
using the EUI-64 protocol.

326
00:17:07,022 --> 00:17:10,017
So at the end of the IP
address when you do not supply

327
00:17:10,017 --> 00:17:14,531
the interface ID, you just do a ::/64,

328
00:17:14,531 --> 00:17:17,932
and then you do EUI-64
as an additional keyword.

329
00:17:17,932 --> 00:17:19,386
I didn't have to do that up here,

330
00:17:19,386 --> 00:17:20,976
because I gave it the interface ID,

331
00:17:20,976 --> 00:17:24,618
but down here, that says
use the special rules,

332
00:17:24,618 --> 00:17:26,911
the special protocol to come up

333
00:17:26,911 --> 00:17:29,925
with an interface ID yourself.

334
00:17:29,925 --> 00:17:32,239
Now you might be wondering,
well, how does he do that?

335
00:17:32,239 --> 00:17:34,324
And actually, we do
need to talk about that,

336
00:17:34,324 --> 00:17:37,113
because your CCNA exams
will expect you to know,

337
00:17:37,113 --> 00:17:41,354
how an EUI-64 interface ID is determined.

338
00:17:41,354 --> 00:17:44,029
So let's take a look at that.

339
00:17:44,029 --> 00:17:47,135
Now as of the time that I'm
doing this recording right here,

340
00:17:47,135 --> 00:17:49,939
we haven't really talked about ethernet.

341
00:17:49,939 --> 00:17:52,601
I've mentioned it here
and there as a layer two

342
00:17:52,601 --> 00:17:55,987
data link layer protocol
that's the most common.

343
00:17:55,987 --> 00:17:58,626
I've said that if you
have a wired nic card

344
00:17:58,626 --> 00:18:00,623
that actually has a wire coming out of it,

345
00:18:00,623 --> 00:18:04,961
99.9% of the time it's going
to be running ethernet.

346
00:18:04,961 --> 00:18:09,539
And I mentioned that all
layer 2 protocols have to have

347
00:18:09,539 --> 00:18:12,727
some kind of a layer 2 address.

348
00:18:12,727 --> 00:18:15,311
You have to have some way
of identifying yourself

349
00:18:15,311 --> 00:18:18,339
on this wire, and in the case of ethernet,

350
00:18:18,339 --> 00:18:20,753
not only does your nic
card have an identifier,

351
00:18:20,753 --> 00:18:23,173
remember we called that
a burned in address,

352
00:18:23,173 --> 00:18:24,540
remember we talked about that,

353
00:18:24,540 --> 00:18:26,474
because it was burned
in by the manufacturer

354
00:18:26,474 --> 00:18:28,132
when it was made?

355
00:18:28,132 --> 00:18:31,022
Well, when I put an
ethernet frame on the wire,

356
00:18:31,022 --> 00:18:33,732
I also have to include
the destination address of

357
00:18:33,732 --> 00:18:38,081
who on this wire it's going
to, and this is a key thing.

358
00:18:38,081 --> 00:18:41,479
When we're talking about
layer 3, the networking layer,

359
00:18:41,479 --> 00:18:44,532
I have a source address,
a source IP address,

360
00:18:44,532 --> 00:18:49,345
my destination layer 3 address
may be somebody on my wire,

361
00:18:49,345 --> 00:18:51,158
but it's probably not.

362
00:18:51,158 --> 00:18:53,698
It's probably somebody on a
completely different network

363
00:18:53,698 --> 00:18:56,353
than me, could be somebody
who's thousands of miles

364
00:18:56,353 --> 00:18:57,893
away from me.

365
00:18:57,893 --> 00:19:02,060
So the source and the destination
IP address usually are not

366
00:19:03,090 --> 00:19:05,385
on the same subnet, on the same network.

367
00:19:05,385 --> 00:19:07,445
Usually they're on different.

368
00:19:07,445 --> 00:19:10,513
At layer 2, though, at layer 2,

369
00:19:10,513 --> 00:19:13,713
the source and destination
layer 2 addresses

370
00:19:13,713 --> 00:19:16,046
have to be on the same wire,

371
00:19:17,099 --> 00:19:18,997
they have to be on the same wire.

372
00:19:18,997 --> 00:19:21,145
Now you might be thinking,
now wait a second Keith,

373
00:19:21,145 --> 00:19:23,637
if my laptop is trying to
communicate to a server

374
00:19:23,637 --> 00:19:25,804
that's across the country,

375
00:19:26,820 --> 00:19:28,673
I can understand how the layer 3 addresses

376
00:19:28,673 --> 00:19:30,593
would be different,

377
00:19:30,593 --> 00:19:33,473
but how could I address my
layer 2 frame to someone

378
00:19:33,473 --> 00:19:37,032
on my wire if I'm not really
trying to get to someone

379
00:19:37,032 --> 00:19:38,425
on my wire, I'm trying to get to someone

380
00:19:38,425 --> 00:19:40,176
across the country?

381
00:19:40,176 --> 00:19:43,953
This is where the router comes into play.

382
00:19:43,953 --> 00:19:47,453
For example, if this was my PC right here,

383
00:19:48,385 --> 00:19:50,450
and let's say my PC had the IP address of

384
00:19:50,450 --> 00:19:54,880
1.1.1.1./24, and somewhere
out there in the world,

385
00:19:54,880 --> 00:19:57,784
we don't know where it is,

386
00:19:57,784 --> 00:19:59,951
is the ine.com web server,

387
00:20:00,870 --> 00:20:05,037
and let's say it had the
address of 7.7.7.7/24,

388
00:20:06,424 --> 00:20:08,753
well if I told my PC,

389
00:20:08,753 --> 00:20:10,384
that's where I need you to go,

390
00:20:10,384 --> 00:20:13,580
the first thing any device
does when it creates a packet

391
00:20:13,580 --> 00:20:16,017
it says, okay, I'm going
to do a quick comparison,

392
00:20:16,017 --> 00:20:19,179
I'm going to compare my
address, my IP address,

393
00:20:19,179 --> 00:20:23,452
or my IPv6 address against
the destination address,

394
00:20:23,452 --> 00:20:26,744
and I'm going to ask myself,
are we in the same network?

395
00:20:26,744 --> 00:20:28,524
Are we in the same subnet?

396
00:20:28,524 --> 00:20:32,039
In this case, the answer
is clearly no, we are not.

397
00:20:32,039 --> 00:20:35,206
I'm trying to get to
7.something, I am 1.something,

398
00:20:35,206 --> 00:20:37,733
we are not in the same subnet.

399
00:20:37,733 --> 00:20:40,463
So now in this case when the answer is no,

400
00:20:40,463 --> 00:20:43,339
the device I'm trying to
reach is not on my cable,

401
00:20:43,339 --> 00:20:44,718
it's not on my subnet,

402
00:20:44,718 --> 00:20:48,279
then the device says okay, well,
how do I get my data there?

403
00:20:48,279 --> 00:20:51,069
Oh, that's what my default gateway is for,

404
00:20:51,069 --> 00:20:54,732
that's what my router is
for, so here's what I'll do.

405
00:20:54,732 --> 00:20:58,732
When I create my packet,
so here's my IP packet,

406
00:21:00,085 --> 00:21:03,936
I'll put a destination of
who I'm trying to reach,

407
00:21:03,936 --> 00:21:06,436
I'll put a source of who I am,

408
00:21:07,662 --> 00:21:10,244
and then when I hand that
down to the data link layer

409
00:21:10,244 --> 00:21:13,258
at layer 2, the data link
layer is going to put

410
00:21:13,258 --> 00:21:15,925
his own header on front of that.

411
00:21:17,157 --> 00:21:21,324
Well, I have a nic card
that connects to this wire,

412
00:21:23,102 --> 00:21:26,435
and that nic card has a layer 2 address.

413
00:21:27,864 --> 00:21:29,148
Now in the case of ethernet,

414
00:21:29,148 --> 00:21:31,304
which is what is used most often,

415
00:21:31,304 --> 00:21:33,917
that address is called a MAC address,

416
00:21:33,917 --> 00:21:37,641
Media Access Control
address, a MAC address.

417
00:21:37,641 --> 00:21:40,470
And just like IPv6
addresses are represented in

418
00:21:40,470 --> 00:21:43,852
hexadecimal, MAC addresses
are represented in

419
00:21:43,852 --> 00:21:45,635
hexadecimals as well,

420
00:21:45,635 --> 00:21:47,749
so it's a good thing we
already know hexadecimal,

421
00:21:47,749 --> 00:21:49,623
because once we get into
the ethernet section we talk

422
00:21:49,623 --> 00:21:51,635
about MAC addresses in more detail,

423
00:21:51,635 --> 00:21:53,956
they'll make more sense.

424
00:21:53,956 --> 00:21:56,564
So a MAC address may look like this.

425
00:21:56,564 --> 00:21:59,952
So that would be the MAC
address of my nic card.

426
00:21:59,952 --> 00:22:02,811
So that was whoever
made my nic card, Intel,

427
00:22:02,811 --> 00:22:05,945
or whoever it is, stamped
that MAC address on it

428
00:22:05,945 --> 00:22:08,030
when they created it.

429
00:22:08,030 --> 00:22:11,242
So anytime a layer 2 frame is going to me,

430
00:22:11,242 --> 00:22:15,423
or coming from me, this
MAC address will be in it.

431
00:22:15,423 --> 00:22:19,590
And similarly, the router has
a MAC address on his nic card

432
00:22:20,681 --> 00:22:22,598
connected to that wire.

433
00:22:23,535 --> 00:22:27,035
Why don't we just say he's 0002:aaaa:bbbb,

434
00:22:28,385 --> 00:22:30,718
because this is hexadecimal.

435
00:22:31,728 --> 00:22:33,125
So now in this particular case,

436
00:22:33,125 --> 00:22:37,961
when ethernet goes to put the
ethernet header on the front,

437
00:22:37,961 --> 00:22:41,890
it will say, trying to give
myself enough room here,

438
00:22:41,890 --> 00:22:45,140
that the destination is 0002:aaaa:bbbb,

439
00:22:48,167 --> 00:22:52,000
and it will say the
source is 00002:1111:2222.

440
00:22:56,919 --> 00:23:00,999
I kind of ran out of room
here, but you get the idea.

441
00:23:00,999 --> 00:23:04,207
So you can see the way this
works is that everything

442
00:23:04,207 --> 00:23:07,928
that's put on the wire at
layer 2 has to be sourced

443
00:23:07,928 --> 00:23:10,760
from the MAC address of the
nic card that created it,

444
00:23:10,760 --> 00:23:14,927
and it has to be going to a
nic card that's on this wire.

445
00:23:16,655 --> 00:23:17,799
So that's what we see here,

446
00:23:17,799 --> 00:23:20,139
it's coming from my MAC address,

447
00:23:20,139 --> 00:23:21,959
going to the MAC address of the router,

448
00:23:21,959 --> 00:23:24,654
so initially when the router
sees this ethernet frame

449
00:23:24,654 --> 00:23:26,106
coming in, he's going to say oh,

450
00:23:26,106 --> 00:23:28,594
somebody's trying to talk to me, okay.

451
00:23:28,594 --> 00:23:31,554
But then when he strips
off this blue section,

452
00:23:31,554 --> 00:23:34,079
he says okay, it looks
like it's me at layer 2,

453
00:23:34,079 --> 00:23:37,188
now let's pass it up the
OSI model to layer 3.

454
00:23:37,188 --> 00:23:38,647
When he strips that off,

455
00:23:38,647 --> 00:23:41,680
he'll say oh, the destination is not me,

456
00:23:41,680 --> 00:23:44,013
it's somebody else, 7.7.7.7.

457
00:23:44,922 --> 00:23:49,322
Okay, as a router, I guess my
job is to route that packet

458
00:23:49,322 --> 00:23:51,239
and send it on its way.

459
00:23:52,468 --> 00:23:54,725
Now why am I talking about MAC addresses

460
00:23:54,725 --> 00:23:57,961
in the context of a video
where we're talking about

461
00:23:57,961 --> 00:23:59,628
IPv6 interface ID's?

462
00:24:00,803 --> 00:24:04,053
Because when you use the EUI-64 keyword

463
00:24:05,002 --> 00:24:07,897
to dynamically come up
with your interface ID,

464
00:24:07,897 --> 00:24:11,767
the MAC address of your
nic card is going to be a

465
00:24:11,767 --> 00:24:14,017
critical component of that.

466
00:24:16,407 --> 00:24:19,301
So let's go back to this.

467
00:24:19,301 --> 00:24:22,910
Given the fact that your
network prefix in IPv6 is

468
00:24:22,910 --> 00:24:27,250
64 bits long, the other
half of the address,

469
00:24:27,250 --> 00:24:31,137
the interface ID, is also 64 bits long.

470
00:24:31,137 --> 00:24:33,823
But if you remember hexadecimal,

471
00:24:33,823 --> 00:24:37,022
each one of these characters
was equal to 4 bits.

472
00:24:37,022 --> 00:24:38,369
Right?

473
00:24:38,369 --> 00:24:40,783
So I'll just write out
the first part of it.

474
00:24:40,783 --> 00:24:42,450
0000:0000:0000:0010.

475
00:24:44,971 --> 00:24:48,054
So that right there encompasses this.

476
00:24:51,923 --> 00:24:54,006
So that is a word, right?

477
00:24:54,865 --> 00:24:57,615
That's 16 bits, 16 times 3 is 48.

478
00:25:00,476 --> 00:25:01,724
48.

479
00:25:01,724 --> 00:25:03,269
Now think about this for a second.

480
00:25:03,269 --> 00:25:06,462
If I say EUI-64, what I'm telling him is,

481
00:25:06,462 --> 00:25:10,063
take your MAC address
and turn it into a 64 bit

482
00:25:10,063 --> 00:25:12,230
interface ID, but he says,

483
00:25:13,458 --> 00:25:17,370
but the number you're giving
me is not a 64 bit number,

484
00:25:17,370 --> 00:25:21,028
it's a 48 bit number, it's too short.

485
00:25:21,028 --> 00:25:24,111
So one of the things that EUI-64 does

486
00:25:25,077 --> 00:25:26,562
is it expands that MAC address

487
00:25:26,562 --> 00:25:29,454
by putting in some
characters in the middle.

488
00:25:29,454 --> 00:25:32,284
So it says, okay, here's
what I'm going to do.

489
00:25:32,284 --> 00:25:33,117
0002:aa,

490
00:25:36,801 --> 00:25:40,551
that's the first half
of the MAC address, aa,

491
00:25:46,348 --> 00:25:47,934
he says okay, here's what I'm going to do,

492
00:25:47,934 --> 00:25:49,649
now that I've split it up,

493
00:25:49,649 --> 00:25:54,009
in order to expand this
out into a 64 bit number,

494
00:25:54,009 --> 00:25:57,592
I'm going to put in
the middle here, ff:fe.

495
00:25:59,647 --> 00:26:02,621
We're not done yet,
but we're almost there.

496
00:26:02,621 --> 00:26:05,087
So this is part of what EUI-64 does,

497
00:26:05,087 --> 00:26:06,763
to dynamically create an interface ID,

498
00:26:06,763 --> 00:26:09,660
it take the MAC address, cuts it in half,

499
00:26:09,660 --> 00:26:12,602
and puts ff:fe in the middle.

500
00:26:12,602 --> 00:26:14,880
So look, we've just taken a 48 bit number,

501
00:26:14,880 --> 00:26:16,168
and what did we do?

502
00:26:16,168 --> 00:26:19,335
We added another 16 bits to it, right?

503
00:26:20,241 --> 00:26:22,566
Because each one of these
characters is 4 bits,

504
00:26:22,566 --> 00:26:26,733
so now, 48 plus 16, now we've
got ourselves a 64 bit number.

505
00:26:28,195 --> 00:26:30,278
But we're not quite done.

506
00:26:31,546 --> 00:26:33,866
In the world of ethernet,

507
00:26:33,866 --> 00:26:37,728
and we'll talk more about this
when we talk about ethernet,

508
00:26:37,728 --> 00:26:38,561
but, 00,

509
00:26:41,950 --> 00:26:45,200
this bit right here has a special name.

510
00:26:48,231 --> 00:26:51,929
That bit is called the individual group,

511
00:26:51,929 --> 00:26:54,661
that's called the Universal Local bit,

512
00:26:54,661 --> 00:26:57,701
or sometimes called the Global Local bit.

513
00:26:57,701 --> 00:27:01,868
And that'll be explained
more in the ethernet section.

514
00:27:03,336 --> 00:27:07,503
It's also sometimes called
Universal/Local bit.

515
00:27:11,343 --> 00:27:13,476
And I'm not really going
to explain right now

516
00:27:13,476 --> 00:27:16,954
why it's important in the
context of Global Local,

517
00:27:16,954 --> 00:27:18,786
Universal Local, but what
I am going to say is when

518
00:27:18,786 --> 00:27:21,128
you're talking about an interface,
when you're talking about

519
00:27:21,128 --> 00:27:25,295
EUI-64, whatever that bit was
in the original MAC address,

520
00:27:26,252 --> 00:27:29,908
it gets changed to just the opposite.

521
00:27:29,908 --> 00:27:34,530
So what we would end up having
happen here is we would have,

522
00:27:34,530 --> 00:27:36,784
I'll do it down here,

523
00:27:36,784 --> 00:27:40,617
so this was the original,
0000:0000:0000:0010,

524
00:27:44,635 --> 00:27:48,718
and then we had aaaa:bbbb,
so that's what we had.

525
00:27:49,563 --> 00:27:51,333
So now what we're going
to do is we're going to

526
00:27:51,333 --> 00:27:54,750
take this bit, and we're going to flip it

527
00:27:56,887 --> 00:27:59,378
to just the opposite.

528
00:27:59,378 --> 00:28:02,159
One little bit change which will give us

529
00:28:02,159 --> 00:28:04,742
0000:0010:0000:0010, aaaa:bbbb.

530
00:28:12,994 --> 00:28:17,516
And so if I convert this
word back into hexadecimal,

531
00:28:17,516 --> 00:28:21,599
that would give me the
numbers of 0202:aaaa:bbbb.

532
00:28:29,885 --> 00:28:33,917
So now when we go back up to our EUI-64,

533
00:28:33,917 --> 00:28:36,445
not only does it have to
split this address in half

534
00:28:36,445 --> 00:28:40,299
and put ff:ee in it, but now
that we've flipped the bit,

535
00:28:40,299 --> 00:28:44,466
our EUI-64 interface ID
becomes 0202:aaff:feaa:bbbb.

536
00:28:54,799 --> 00:28:58,791
And that is what would be
applied to the second portion

537
00:28:58,791 --> 00:29:02,922
of the IPv6 address as the,
what we used to call host bits,

538
00:29:02,922 --> 00:29:06,305
but we now call the interface ID.

539
00:29:06,305 --> 00:29:09,096
So let's do an example of this,
let me give you an exercise

540
00:29:09,096 --> 00:29:12,293
and see if you can figure this out.

541
00:29:12,293 --> 00:29:16,460
You might want to take a
screenshot of this real quick.

542
00:29:18,375 --> 00:29:21,708
Alright, so, here is a laptop let's say.

543
00:29:24,536 --> 00:29:28,536
And it's MAC address is
equal to 021a:5555:6677,

544
00:29:38,329 --> 00:29:40,070
and on that laptop,

545
00:29:40,070 --> 00:29:44,237
you say IPv6 address
2001:2222:3333:4444::/64,

546
00:29:53,409 --> 00:29:55,409
and then you say EUI-64.

547
00:29:57,502 --> 00:29:59,890
So now my question to you is,

548
00:29:59,890 --> 00:30:02,416
what will the full address be?

549
00:30:02,416 --> 00:30:04,829
When it creates the interface ID,

550
00:30:04,829 --> 00:30:07,736
what will be the full address?

551
00:30:07,736 --> 00:30:10,196
Pause the video, and then
press play when you think

552
00:30:10,196 --> 00:30:12,029
you've figured it out.

553
00:30:14,508 --> 00:30:17,331
Alright, so, it doesn't really matter

554
00:30:17,331 --> 00:30:18,931
which order we take it,

555
00:30:18,931 --> 00:30:20,855
I'm going to do the bit flipping first.

556
00:30:20,855 --> 00:30:23,011
So it's going to be flipped right here,

557
00:30:23,011 --> 00:30:25,761
so we know that 02 is 0000, 0010,

558
00:30:28,289 --> 00:30:30,929
and we know that it's this bit,

559
00:30:30,929 --> 00:30:35,868
the Universal Local bit
that's going to be changed,

560
00:30:35,868 --> 00:30:39,035
so that will be changed to 0000, 0000,

561
00:30:43,132 --> 00:30:47,040
that's going to be the
change, okay so now,

562
00:30:47,040 --> 00:30:50,040
we've gone to 001a, instead of 021a,

563
00:30:55,303 --> 00:30:58,184
it's been now changed to 001a,

564
00:30:58,184 --> 00:31:02,267
:55, and now we've got to
put the ff:fe in there,

565
00:31:04,195 --> 00:31:05,028
ff:fe,

566
00:31:07,677 --> 00:31:11,760
and then we put the
remainder of the MAC address,

567
00:31:12,994 --> 00:31:13,827
55:6677.

568
00:31:16,968 --> 00:31:19,475
So that is the answer,

569
00:31:19,475 --> 00:31:22,808
by using EUI-64 this is the interface ID

570
00:31:24,401 --> 00:31:26,097
that it comes up with.

571
00:31:26,097 --> 00:31:29,014
(electronic music)