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(futuristic music)

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- So here we're gonna talk

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about something called the IPv6
Neighbor Discovery process,

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which is actually a combination
of several IPv6 packets

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working together to perform special roles.

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In the previous video, I
talked about five special

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or distinguishable
types of IPv6 addresses.

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We talked about link-local.

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We talked about multicast,
and a couple of others,

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and I mentioned that there
was one more special one

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that I want to get to,

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but in order to understand that last one,

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we have to understand this first.

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And then once I go through this,

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then my last video on sort
of IPv6 general theory

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will be on that final, special address

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I've been holding back.

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So lets talked about
IPv6 Neighbor Discovery.

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We've talked, as far as layer
four protocols are concerned,

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we've really focused
pretty much exclusively

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on TCP and UDP, but I have
hinted in some previous slides

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that there were others, as well.

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Well, one of them that you
definitely need to be aware of,

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that's a layer four and
above protocol, is ICMP,

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the internet control
messaging protocol, ICMP,

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internet control messaging protocol.

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So the most common usage of ICMP

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is when people issue the ping command.

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For example, and you can do this

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on your own laptop, as well.

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If I open up my command prompt,

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bring it over here.

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And a lot of times, if
you wanna figure out

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if you have network
connectivity to something,

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for example, I know that
Google's DNS server,

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a server that Google owns
that can resolve websites

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to IP addresses, is 8.8.8.8.

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That's very common knowledge.

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It's public knowledge.

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And so if I wanna see if I
can actually have connectivity

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to that, I can type ping and
then type in that IP address

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and hit enter.

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So clearly, now I'm getting a reply.

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So what was just happening right there?

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So when you type ping, what's
actually happening is the CPU

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of your device, of my laptop in this case,

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is creating an ICMP message,

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and ICMP has several
different kinds of messages,

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depending on what the objective is.

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So in this particular case,
my laptap was creating

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what was called an ICMP
echo request, echo request.

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Basically, it sending out
an echo request to 8.8.8.8,

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and if that server is also running ICMP,

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which most devices do by default,

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it will turn around and send back

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to me what's called an ICMP echo reply,

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and that's what we see right here.

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We see that the first one
timed out for some reason,

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but then I got three echo replies.

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So this was an echo
request going out from me.

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I actually send four echo requests,

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and I got a response
back from three of them.

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So that was just an
example of ICMP in action.

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Now, there are other
ICMP messages, as well.

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I don't have time to get into
all of them in this course,

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but I would definitely
recommend that you Google

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the term ICMP and just
be familiar with the,

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there's about maybe five,

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four or five different ICMP messages,

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and I've just talked about the top two,

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echo request, echo reply.

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What does that have to do with this?

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Well, just like I mentioned
a couple slides back

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or a couple videos back, that
DHCP had been upgraded for v6,

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that there's a DHCPv6.

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Well, there's an ICMPv6.

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Now, this is kind of interesting
when you think about it

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because ICMP, because it's layer four,

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rides behind an IP header.

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So in other words, you've
got your IP header here,

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and then ICMP is like in the
payload of the IP packet.

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So one would wonder why did
they have to update ICMP?

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Well, for one thing, if
they had not updated it,

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there'd be no way to ping an IPv6 address

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because within the body
of the ICMP message,

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it says who am I trying to talk to?

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So not only is the
destination in the header

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of the IP packet itself,

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but the destination you're trying to ping

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is also in the body of the ICP message,

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saying I'm trying to do
an echo request to you.

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Can you please respond back?

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It's in the body of the packet.

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So they had to upgrade ICMP, as well,

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in order to be able to
handle IPv6 addresses.

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In addition to doing that,
when they updated ICMP,

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they actually added some
new ICMP message types

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that did not exist before.

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So in addition to echo
request and echo reply,

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which still exist,

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they also created four new
types of ICMPv6 messages,

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which are only applicable for IPv6,

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and those are Neighbor Solicitation,
Neighbor Advertisement,

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Router Solicitation, and
Router Advertisement.

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All four of those are in the
body of an ICMPv6 packet.

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In the header of the ICMPv6
packet, in the header,

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there's a little type code,
and the type code indicates

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what kind of ICMP message is this.

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Is this an echo request?

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Is it an echo reply?

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Or there are other type codes
for these things right here.

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So these specific ICMPv6
message types together,

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we call them the Neighbor
Discovery Protocol.

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So if you hear that term,
which you most likely will,

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the IPv6 Neighbor Discovery Protocol,

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that should key off in
your head, oh, okay,

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they're talking about how we
use these four different kinds

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of ICMPv6 messages.

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So lets talk about how this process works.

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And what I'm gonna
specifically gonna refer to

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is back when I was talking
about IPv6 addresses,

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and I was first introducing
the concept of an IPv6 address,

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I said that a device could have

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a statically configured IPv6 address.

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I said it could learn about
it from a DHCPv6 server

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or there was something special in IPv6

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called stateless address
automatic configuration,

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or SLAAC, S-L-A-A-C,

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and this, these messages
that we see right here

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are how our stateless address
automatic configuration works.

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Let's whiteboard that process,

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so you can see what's going on.

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Okay, so lets start with our laptop.

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And the laptop has a network
interface card, a NIC.

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And then all of a sudden,
it's connected to a cable.

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And there's something at the
other end of this cable here.

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I'm not gonna tell you what it is,

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but whatever it is, it's
generating electrical signal

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so the NIC card on this
PC says, aha, okay,

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I've been connected to a network.

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I know I'm connected to a network.

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Now, this NIC card is enabled for IPv6.

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That's one of the protocols that's on it.

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As a matter of fact, all
Windows devices these days

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have IPV6 enabled on their NIC cards.

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You probably didn't even know it,

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but you're running IPv6.

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Now we know that a NIC
card, because it's connected

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to an ethernet segment,

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has a burned in address
called a MAC address.

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So let's put my MAC address on here.

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0002.1111.2222.

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Alright, so that's the MAC
address of this NIC card.

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So very first thing
this NIC card has to do,

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once it enables itself for IPv6,

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is it has to create a
link-local address for itself.

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Do you remember, review question,

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how do we recognize
link-local addresses in IPv6?

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Well, hopefully you said,
ah, those are the addresses

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that begin with fe80.

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You're absolutely right.

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So we'll begin with fe80,
but before I add that,

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we have to convert this
into an EUI-64 interface ID.

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I'm not gonna explain it.

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We already did that in a previous video,

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so all I'll say is that
my link-local address

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will end up being
fe80::0202:11ff:fe11:2222.

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So that's gonna be my link-local address.

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Starts out with fe80,

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and then we use the EUI-64
format to convert this

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into an interface ID.

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Now, one thing I wanna make
you aware of right now.

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Several years back,
there were some engineers

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from various different
disciplines and companies

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who decided that creating an interface ID

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out of a MAC address
might be kind of insecure

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because they said, hey,
if somebody was monitoring

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your traffic and they always saw

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the exact same interface ID,

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they could track where you were.

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They could say, oh, we
can see this guy moved

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around through the
building throughout the day

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because we can see this link-local,

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we can see this interface ID,

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this same interface ID moving around.

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So because, just like IP version 4 right?

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When you move from one
subnet to the other,

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you get a new address via DHCP.

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Well, same thing is true with IPv6.

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If I'm sitting in Payroll right now,

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I'll have some sort of IPv6 network

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that belongs to Payroll,
but my interface ID

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will still be based off of my MAC address

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if I'm using EUI-64.

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Now if I pick up my laptop and I go over

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to the Marketing Department,
well, now my IPv6 prefix

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has changed because I did DHCP,

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and now I'm sitting in their subnet,

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but my interface ID has not changed.

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If it's using EUI-64, it is still the same

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'cause my MAC address goes
with me wherever I go.

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So some people said, huh,

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well, that means if somebody has

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some network monitoring equipment set up

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like in a building or something,

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watching all the packets everywhere,

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they could say, oh, interesting.

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We see the interface ID here of Joe.

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It's his MAC address,
and we see it traveling

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throughout the building.

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Even though the prefix
is changing, we can track

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where Joe is going because we
can see that same interface ID

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never changing as it moves
around through the network.

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So these engineers came
up with a different,

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I don't know what the RFC is.

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It's not off the top off my head,

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but there's an RFC that's
been out for a while now

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that says basically, when a
device dynamically comes up

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with an interface ID, it should just be

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some like random number,

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and it should change it
every once in a while.

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Like every hour or so,
it should change it,

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so that it can't be tracked.

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So the reason I'm saying that to you

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is because if you look at the
IPv6 address on your laptop,

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chances are your interface
ID will probably not be

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the EUI-64 format.

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It probably will not be
related to your MAC address.

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It's probably running this newer standard

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that says it needs to
be some random number

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that changes over time.

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But you do need to know

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how EUI-64 interface IDs are created,

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especially on Cisco devices

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because it's a keyword that
you can use on a Cisco device,

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and every single Cisco device,

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when it creates a link-local
address for itself,

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it's always based off
of the EUI-64 format.

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Cisco routers and switches,

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they don't use this
randomized interface ID thing

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that Microsoft Windows and other hosts do.

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They always use EUI-64.

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So enough said about that.

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This device right here
creates a link-local address

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for itself, and it says,
alright, first thing I need to do

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is I need to make sure
that on this segment

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there's nobody else that's using

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this exact same link-local address.

249
00:12:24,207 --> 00:12:26,893
I have to make sure that
there are no duplicates,

250
00:12:26,893 --> 00:12:28,560
that this is unique.

251
00:12:29,439 --> 00:12:32,733
So he'll send out his very first type

252
00:12:32,733 --> 00:12:35,951
of Neighbor Discovery Packet,

253
00:12:35,951 --> 00:12:37,534
which is an ICMPv6.

254
00:12:39,993 --> 00:12:42,743
We call it Neighbor Solicitation,

255
00:12:45,778 --> 00:12:48,945
and the source will be his link-local,

256
00:12:50,479 --> 00:12:52,146
and the destination,

257
00:12:54,079 --> 00:12:56,132
the destination will be something called

258
00:12:56,132 --> 00:12:59,049
a solicited node multicast address.

259
00:12:59,937 --> 00:13:02,013
Now, that is that special type of address

260
00:13:02,013 --> 00:13:03,605
I have not talked to you about.

261
00:13:03,605 --> 00:13:06,545
I said there was one remaining
address that was unique,

262
00:13:06,545 --> 00:13:07,834
that we hadn't talked about.

263
00:13:07,834 --> 00:13:11,137
That's it, and in the next
video, I'll talk about this.

264
00:13:11,137 --> 00:13:12,999
But I want to start out by explaining

265
00:13:12,999 --> 00:13:16,066
where this special address is used,

266
00:13:16,066 --> 00:13:19,566
and then we can look at how is it created.

267
00:13:20,815 --> 00:13:24,430
Now, if anybody did have
this link-local address here,

268
00:13:24,430 --> 00:13:25,869
what I will tell you

269
00:13:25,869 --> 00:13:28,081
is that the solicited
node multicast address

270
00:13:28,081 --> 00:13:30,581
is actually derived from this.

271
00:13:31,761 --> 00:13:33,321
It's derived from that,

272
00:13:33,321 --> 00:13:35,656
so that if somebody on
this wire actually did have

273
00:13:35,656 --> 00:13:37,609
this exact same link-local address,

274
00:13:37,609 --> 00:13:40,401
which is highly unlikely,

275
00:13:40,401 --> 00:13:43,183
then they would actually
listen to this packet,

276
00:13:43,183 --> 00:13:45,668
and they would respond back.

277
00:13:45,668 --> 00:13:47,835
So hopefully, nobody does,

278
00:13:49,188 --> 00:13:51,747
and so he says, okay.

279
00:13:51,747 --> 00:13:54,707
Now if somebody did respond back,

280
00:13:54,707 --> 00:13:56,457
I'm gonna erase this,

281
00:13:57,423 --> 00:14:01,590
somebody would respond back
with a Neighbor Advertisement.

282
00:14:07,984 --> 00:14:10,677
So that's another part of the
Neighbor Discovery Process,

283
00:14:10,677 --> 00:14:13,423
Neighbor Solicitation and
Neighbor Advertisement.

284
00:14:13,423 --> 00:14:15,805
But in this particular
case, we don't wanna see

285
00:14:15,805 --> 00:14:17,284
a Neighbor Advertisement come back

286
00:14:17,284 --> 00:14:21,329
because that would mean uh-oh,
somebody's got our address.

287
00:14:21,329 --> 00:14:23,297
So this process right now

288
00:14:23,297 --> 00:14:26,591
of where we're basically
sending out a packet saying,

289
00:14:26,591 --> 00:14:29,031
hey, is anybody using my address?

290
00:14:29,031 --> 00:14:33,199
It actually goes by a name that
you should be familiar with.

291
00:14:33,199 --> 00:14:36,532
It's called Duplicate Address Detection,

292
00:14:39,450 --> 00:14:41,515
Duplicate Address Detection.

293
00:14:41,515 --> 00:14:46,025
So whenever an IPv6 node
either dynamically comes up

294
00:14:46,025 --> 00:14:48,315
with an address for itself

295
00:14:48,315 --> 00:14:50,697
or you statically configure one on there,

296
00:14:50,697 --> 00:14:52,377
it always does this.

297
00:14:52,377 --> 00:14:54,715
It sends out a Neighbor
Solicitation packet,

298
00:14:54,715 --> 00:14:56,217
basically for itself, saying,

299
00:14:56,217 --> 00:14:59,250
hey, is anybody out there using this?

300
00:14:59,250 --> 00:15:03,261
Most of the time, probably
99.99% of the time,

301
00:15:03,261 --> 00:15:04,883
nothing should come back.

302
00:15:04,883 --> 00:15:06,255
So you have completed

303
00:15:06,255 --> 00:15:10,243
the Duplicate Address Detection process.

304
00:15:10,243 --> 00:15:13,923
Okay, now, this PC says, okay, great,

305
00:15:13,923 --> 00:15:16,621
I've got a link-local address.

306
00:15:16,621 --> 00:15:20,011
So the next thing it says is
I need to get a global prefix.

307
00:15:20,011 --> 00:15:23,677
If I'm ever gonna get off this
link and send IPv6 packets

308
00:15:23,677 --> 00:15:27,063
to other departments or even the internet,

309
00:15:27,063 --> 00:15:29,355
I need a global address to do that.

310
00:15:29,355 --> 00:15:32,857
And he says, well, I've
been configured for SLAAC,

311
00:15:32,857 --> 00:15:36,457
for stateless address
automatic configuration.

312
00:15:36,457 --> 00:15:39,374
So what he does is now he sends out

313
00:15:40,974 --> 00:15:44,057
another type of ICMP message, ICMPv6,

314
00:15:46,987 --> 00:15:50,154
which is called a Router Solicitation,

315
00:15:51,629 --> 00:15:53,462
Solicit, Solicitation.

316
00:15:55,889 --> 00:16:00,729
And once again, the source
is gonna be his link-local,

317
00:16:00,729 --> 00:16:04,062
and the destination is gonna be FF02::2.

318
00:16:09,043 --> 00:16:12,193
Now, FF, you should be
able to recognize that.

319
00:16:12,193 --> 00:16:14,090
That's one of those patterns
I said you should recognize.

320
00:16:14,090 --> 00:16:16,423
That is a multicast address,

321
00:16:17,359 --> 00:16:20,146
and this multicast address
has special meaning.

322
00:16:20,146 --> 00:16:23,979
This is called the All
IPv6 Routers multicast,

323
00:16:25,321 --> 00:16:29,359
so any router that's
enabled to IPv6 is listening

324
00:16:29,359 --> 00:16:32,192
for packets going to this address.

325
00:16:33,051 --> 00:16:34,729
So let' say there is a router.

326
00:16:34,729 --> 00:16:36,979
Hopefully there is one.

327
00:16:36,979 --> 00:16:39,181
Let's put him right here,

328
00:16:39,181 --> 00:16:41,193
and let's say that on
that router's interface,

329
00:16:41,193 --> 00:16:44,943
I have configured the
following IPv6 address.

330
00:16:50,699 --> 00:16:51,747
Okay?

331
00:16:51,747 --> 00:16:54,010
So looking at that, remember,

332
00:16:54,010 --> 00:16:58,177
how much of this IPv6 address
is the prefix, the network?

333
00:16:59,490 --> 00:17:00,842
The first 64 bits.

334
00:17:00,842 --> 00:17:02,690
That's what this subnet
mask is telling us,

335
00:17:02,690 --> 00:17:04,968
which is all of this right there.

336
00:17:04,968 --> 00:17:07,070
That's the prefix.

337
00:17:07,070 --> 00:17:08,461
So when this router receives

338
00:17:08,461 --> 00:17:11,211
this Router Solicitation message,

339
00:17:13,364 --> 00:17:18,289
he responds back with, you
can probably guess what it is.

340
00:17:18,289 --> 00:17:20,206
A Router-Advertisement.

341
00:17:27,357 --> 00:17:30,190
And he sends it back to that node.

342
00:17:31,189 --> 00:17:34,022
I'm trying to make some room here.

343
00:17:35,014 --> 00:17:38,681
Destination= fe80::0202:11ff:fe11:2222.

344
00:17:46,007 --> 00:17:48,974
So it's going back to that host.

345
00:17:48,974 --> 00:17:52,891
And the source is, see
if I can fit it in here,

346
00:17:55,156 --> 00:17:57,739
the router's link-local address

347
00:18:00,523 --> 00:18:03,273
because this router also has one.

348
00:18:09,877 --> 00:18:11,796
So whatever his link-local address is,

349
00:18:11,796 --> 00:18:14,604
that is what the source of this will be.

350
00:18:14,604 --> 00:18:16,101
And here's the great thing.

351
00:18:16,101 --> 00:18:20,564
Inside this Router-Advertisement,
in the body of it,

352
00:18:20,564 --> 00:18:24,775
he says, hey, let me tell
you what prefixes I have

353
00:18:24,775 --> 00:18:26,275
on this interface.

354
00:18:30,964 --> 00:18:34,649
Now that the host sees that,
that Router-Advertisement,

355
00:18:34,649 --> 00:18:36,638
he says, oh, very cool.

356
00:18:36,638 --> 00:18:39,684
I know what the global prefix
is that lives on this wire,

357
00:18:39,684 --> 00:18:42,603
so I can use stateless address
automatic configuration

358
00:18:42,603 --> 00:18:46,389
to come up with my own global address.

359
00:18:46,389 --> 00:18:48,577
I'll just use that 'cause after all,

360
00:18:48,577 --> 00:18:49,789
that's what the router's using,

361
00:18:49,789 --> 00:18:53,298
and I gotta be on the
same thing as the router,

362
00:18:53,298 --> 00:18:56,798
and then, I will use the same interface ID

363
00:18:58,637 --> 00:19:00,009
that I got in my link-local.

364
00:19:00,009 --> 00:19:03,336
I'll just do the EUI-64 process again,

365
00:19:03,336 --> 00:19:06,503
which will end up with the same thing.

366
00:19:10,089 --> 00:19:12,021
And then, once he has this,

367
00:19:12,021 --> 00:19:15,210
he will do Duplicate
Address Detection on this.

368
00:19:15,210 --> 00:19:18,341
He'll send out a Neighbor
Solicitation message for this.

369
00:19:18,341 --> 00:19:20,215
Shouldn't hear anything back,

370
00:19:20,215 --> 00:19:23,132
and now he knows that it is unique.

371
00:19:24,131 --> 00:19:27,884
So this is how stateless
address automatic configuration

372
00:19:27,884 --> 00:19:31,003
works, or Address Autoconfig.

373
00:19:31,003 --> 00:19:32,924
Basically, you gotta come
up with a link-local address

374
00:19:32,924 --> 00:19:36,375
for yourself first, verify
that there's no duplicates

375
00:19:36,375 --> 00:19:38,363
by sending a Neighbor Solicitation message

376
00:19:38,363 --> 00:19:40,177
to yourself essentially.

377
00:19:40,177 --> 00:19:42,804
Then you send out a Router Solicitation

378
00:19:42,804 --> 00:19:45,804
to this reserved address of FF02::2.

379
00:19:47,069 --> 00:19:49,429
All routers are supposed
to listen to that.

380
00:19:49,429 --> 00:19:50,742
When the router hears it,

381
00:19:50,742 --> 00:19:53,444
he sends a Router-Advertisement back.

382
00:19:53,444 --> 00:19:56,262
He sends it to you,
your link-local address,

383
00:19:56,262 --> 00:19:58,338
and in the body of that message, he says,

384
00:19:58,338 --> 00:20:00,551
here's the global prefix
at everybody on this wire,

385
00:20:00,551 --> 00:20:04,371
here's the group that you're
a part of, the subnet,

386
00:20:04,371 --> 00:20:07,517
and now the PC can use that prefix,

387
00:20:07,517 --> 00:20:10,364
once again, create his own interface ID,

388
00:20:10,364 --> 00:20:13,416
and now he has a global
prefix that he can use

389
00:20:13,416 --> 00:20:16,869
to speak to the rest of the world.

390
00:20:16,869 --> 00:20:18,869
Now, there is one other,

391
00:20:19,724 --> 00:20:21,377
there's a couple of additional
things about this here

392
00:20:21,377 --> 00:20:23,377
that I wanna talk about.

393
00:20:24,339 --> 00:20:26,098
This address is special.

394
00:20:26,098 --> 00:20:28,977
Let me put a red circle around it.

395
00:20:28,977 --> 00:20:31,309
Definitely wanna memorize that.

396
00:20:31,309 --> 00:20:34,976
And every single IPv6
host is also listening

397
00:20:37,013 --> 00:20:40,516
to another special multicast address.

398
00:20:40,516 --> 00:20:43,933
I'll write that on the bottom, I suppose.

399
00:20:45,913 --> 00:20:47,746
That would be FF02::1.

400
00:20:50,246 --> 00:20:53,163
That is the All IPv6 Hosts Address,

401
00:20:56,142 --> 00:20:57,635
and the router's listening to that,

402
00:20:57,635 --> 00:21:00,885
so actually this router is listening to

403
00:21:03,661 --> 00:21:05,796
four addresses, right?

404
00:21:05,796 --> 00:21:07,994
The router's got his link-local.

405
00:21:07,994 --> 00:21:10,001
He's listening to anybody
who wants to talk to him

406
00:21:10,001 --> 00:21:11,773
on his global prefix.

407
00:21:11,773 --> 00:21:13,860
He's listening to anybody
who wants to send something

408
00:21:13,860 --> 00:21:16,893
to him specifically as
just a generic router,

409
00:21:16,893 --> 00:21:19,823
and he is considered a host.

410
00:21:19,823 --> 00:21:22,775
Any NIC card that has IPv6
on it is considered a host,

411
00:21:22,775 --> 00:21:26,314
so he's listening to
the All Hosts Address.

412
00:21:26,314 --> 00:21:29,314
So everybody at minimum, at minimum,

413
00:21:31,112 --> 00:21:34,945
devices are listening
to three IPv6 addresses,

414
00:21:36,793 --> 00:21:40,126
their link-local, the All Hosts Address,

415
00:21:41,211 --> 00:21:44,051
and the solicited node multicast address.

416
00:21:44,051 --> 00:21:46,491
Now, I know that I haven't
defined that one for you yet.

417
00:21:46,491 --> 00:21:48,830
That'll be in the next video.

418
00:21:48,830 --> 00:21:52,701
But every device has a solicited
node multicast address,

419
00:21:52,701 --> 00:21:56,235
and that's derived from
the link-local address,

420
00:21:56,235 --> 00:21:57,461
and they're also listening

421
00:21:57,461 --> 00:22:00,378
to the All Hosts multicast address.

422
00:22:01,451 --> 00:22:03,250
Now, whether or not they
have a global prefix,

423
00:22:03,250 --> 00:22:04,701
they may or they may not.

424
00:22:04,701 --> 00:22:07,098
I mean, if they wanna
get off of their subnet,

425
00:22:07,098 --> 00:22:11,616
they're gonna need one,
but it's not mandatory.

426
00:22:11,616 --> 00:22:14,123
And routers also listen to
this other special address

427
00:22:14,123 --> 00:22:17,494
of the All IPv6 router's address.

428
00:22:17,494 --> 00:22:20,411
(futuristic music)