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(upbeat music)

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- So the title of this video I recognize

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looks a little strange, ARP and
the IPv6 Solution (chuckles)

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but in order for me to
really talk about the

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Solicited Node Multicast address,

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we first have to understand
something that happens

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in the world of IP version
four which is called ARP

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or the Address Resolution Protocol.

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Haven't really discussed it
up until now, but we need

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to understand this so that
the Solicited Node Multicast

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address will make some more sense.

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So let's go back to our
whiteboard here for a moment.

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Let's assume that this is your laptop.

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This is you.

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This is you on a network.

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And here is a laptop
connected to a router.

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And somewhere on here was DHCP Server.

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Usually the DHCP Server is
not actually on your wire,

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but just to make the
drawing a little bit easier

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I'm gonna do it.

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Okay so the router has a
network interface card,

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an Ethernet NIC, just like
you have an Ethernet NIC.

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And his Ethernet NIC
has a MAC address on it

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that was created by the manufacturer.

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Let's say the MAC address
is 0011:2222:3333.

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And because he's a router,
we have statically configured

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an IP address on him, 2.2.2.2/24.

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Okay, now your NIC card also
has a MAC address on it.

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Every NIC card does.

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Let's say that's yours.

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And let's say after doing DHCP process

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and obtaining an IP address,
you learned this information.

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You learned that your
IP address is 2.2.2.1

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and your learned that your
default gateway was 2.2.2.2.

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So you learned all this via DHCP.

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Okay, statistics show that

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when a laptop creates traffic

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or a tablet or a smartphone,
people have done studies

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trying to answer the question
what percentage of traffic

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that a laptop creates is destined
for its own local subnet,

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and what percentage of traffic
is destined for other subnets

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or the rest of the world.

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And most of the time it's 20, 80.

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In other words, roughly 20% of
the traffic that you generate

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is for your own local network,
and 80% of the traffic

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is going out to the rest of the world.

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So we know that this PC
right here at some point

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he's gonna want to bring up
a webpage or he's gonna want

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to open up his email program.

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He's gonna open up something
where he's gonna want

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to send a packet to the outside world.

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So let's say the PC does
something like this.

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So here's a little
thought bubble from the PC

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and he says, "I want to go to the website

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"that is at 7.7.7.7.

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"That is NOT on my own subnet!!"

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Because remember he
always says a comparison

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of his source address and the destination

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of where he wants to go.

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In this case he's saying,
"Okay, that's not me.

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"That's not here."

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He says, "Okay, well, I'm
gonna create my packet anyway."

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He says, "Okay, here we
go, here's my IP packet,

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"and the source of the IP packet

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"is gonna be me, 2.2.2.1."

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The destination is gonna be 7.7.7.7.

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And then he says, "When I send that down

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"to the Ethernet NIC card,
the NIC card is gonna have

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"to put that into an Ethernet frame."

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And an Ethernet frame has a
source and destination MAC.

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He says, "All right, well the source MAC,

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"that's pretty easy, that's mine."

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And the destination is,

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huh, well, he says,

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"I know that when I
create an Ethernet frame,

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"the destination of the
frame has to be somebody

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"on my wire."

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And he says, "But ultimately
the person I'm trying to reach

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"is not on my wire.

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"They're not in my subnet."

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And so the PC says, "Well,
is there anybody on my wire

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"that might know how to get here?

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"Oh, yeah, the router,
that's why I have him

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"in the first place, the default-gateway."

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So he says, "What I
should do is at layer two,

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"I should destine my Ethernet MAC address

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"to the MAC address of the router."

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That way the router will
pick up this Ethernet frame

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and when he sends it up the
stack to the networking layer

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then he'll realize that it's
a packet that's not for him

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that needs to be routed.

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He says, "But, huh, interesting.

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"I know the router's IP
address, but I don't know

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"his layer two address.

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"How am I gonna resolve that address?"

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That's where he kicks in
and uses something called

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the Address Resolution Protocol, ARP,

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and this is what ARP was designed to do.

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When you know the layer
three address of someone

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in your subnet, and that's the key.

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ARP is only used when you're
trying to resolve someone

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in your subnet.

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For example, he would
never ARP for 7.7.7.7

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because that device is
clearly not on this wire.

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So when you're trying to
reach someone in your subnet

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and you know their layer three address,

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but you don't know their
layer two MAC address,

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this is where we use ARP.

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So with ARP, it would look like this.

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This packet would be put on hold.

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You'd have to put it in
memory and store it in memory.

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And he would create what's
called an ARP Request.

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And the source would be himself,

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and the destination would be the router

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he's trying to talk to.

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And an ARP request actually
has a few more fields than that

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but we'll just keep it simple.

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And then he would create
his layer two header.

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And the source of his layer
two header would be himself,

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0011:3333:4444,

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and the destination would be a broadcast.

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And a broadcast MAC address is all ones,

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or ffff in hexadecimal.

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So that is a special MAC address.

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That is the broadcast MAC address.

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It's for everybody on the wire.

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And that's what the layer
two frame would look like.

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Everybody on the wire would see it.

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Everybody would say, "Oh this is for me."

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But when everybody is stripped
off this layer two header

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revealing what was behind
it, they would recognize,

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"Oh, this isn't for
me, except the router."

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The router would say,
"Oh, somebody's sending

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"an ARP request to me, alright."

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Guess what he's gonna send back?

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He's gonna send, I'm
not gonna draw it here,

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I'm just gonna write the name of it.

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He would send back an ARP Response.

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And in that response he
would say, "I am 2.2.2.2.

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"My MAC is

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"0011:2222:3333."

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When we know someone's layer three address

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who is in our subnet but we
don't know their layer two

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address and we need to talk
to them, this is the process.

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We send out a broadcast to
everybody called an ARP Request.

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But inside the body of that packet we say,

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"Hey, this is the guy I'm
actually looking for."

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And if that guy actually exists,

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he sends back an ARP
Response directly to us

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giving us his MAC address.

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And now that the MAC address
is known, this packet,

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which has been waiting
forever up here to go

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to the web server, we can
now actually address it

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at layer two to the router,

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and away it goes.

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Now the laptop can put this on the wire.

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The router at layer two
will think it's for him,

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so he will pick it up, and
everybody else on this wire

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will ignore it.

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And then when the router strips
off the layer two header,

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he'll see this and recognize
that it's not for him.

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Now what in the world does
this have to do with IPv6

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and why is this grouped
in with the IPv6 videos?

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The reason I want to bring
this up is because this is

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a classic case in the
world of IP version four

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of usage of a broadcast.

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In IP version four there's
a lot of things that go out

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as broadcasts.

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ARP Requests are one of them.

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You see ARP Requests all the
time all day long on networks.

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ARP Requests go out as broadcasts,

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and there's a lot of
other stuff that goes out

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as broadcasts as well.

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Well in the case of IPv6,
in this exact same process

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where the laptop would say,
"I know the IPv6 address

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"of my router.

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"What I don't know is his MAC address."

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You might be tempted to
think, "Oh, well there must be

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"an ARP v6", and there's
where your mistake would be.

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There is no such thing as
ARP in the world of IPv6.

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As a matter of fact, when
I was showing you all those

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different types of IPv6
messages, Link-Local, global,

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site local, did I ever
show you an IPv6 address

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that was a broadcast address?

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No, I didn't, because they don't exist.

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There's no such thing
as a broadcast address

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in the world of IPv6.

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So think about that for a second.

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In this case we needed to figure out

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what his MAC address was.

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And since we didn't know
it, and we had to create

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an Ethernet frame, and an
Ethernet frame requires

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a destination MAC address,
but we didn't know

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the destination MAC address.

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So what did we do?

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We just broadcast it.

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So how is IPv6 gonna do this
if there's no such thing

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as a broadcast?

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00:10:38,848 --> 00:10:42,619
This is where that Solicited
Node Multicast address

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00:10:42,619 --> 00:10:44,670
comes into play.

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00:10:44,670 --> 00:10:48,253
What I'm gonna do is
I'm going to save this

202
00:10:49,503 --> 00:10:51,675
so I can refer back to it,

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00:10:51,675 --> 00:10:55,092
but then I'm going to change it, IPv6 ND,

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and we're gonna replace it with IPv6.

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00:11:09,613 --> 00:11:11,007
Okay, so here we are.

206
00:11:11,007 --> 00:11:14,462
Now let's go ahead and
replace some of this stuff.

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00:11:14,462 --> 00:11:17,295
Okay, so let's say that the router

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00:11:21,316 --> 00:11:25,044
now has, I'm gonna give him
a really small IPv6 address.

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00:11:25,044 --> 00:11:29,211
It's mostly zeros so I can
condense it down, 2001::1.

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So most of the bits in this
128-bit address are zeros.

211
00:11:39,150 --> 00:11:42,396
And we also know he's got to
have a Link-Local address.

212
00:11:42,396 --> 00:11:45,396
Let's just make that simple as well.

213
00:11:47,118 --> 00:11:51,766
And we know he's listening
to the all routers address

214
00:11:51,766 --> 00:11:52,995
which is that.

215
00:11:52,995 --> 00:11:57,352
And we know he's listening
to the all hosts address,

216
00:11:57,352 --> 00:11:58,519
which is that.

217
00:11:59,663 --> 00:12:03,830
Now there's another address
that he's listening to.

218
00:12:06,105 --> 00:12:10,631
Let me change his Link-Local
just a little bit,

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00:12:10,631 --> 00:12:11,464
fe80::

220
00:12:14,722 --> 00:12:15,555
0011:11ff:

221
00:12:19,205 --> 00:12:20,038
fe33:4444.

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00:12:23,742 --> 00:12:26,149
All right, so let's say that
this is a Link-Local address

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00:12:26,149 --> 00:12:30,373
and this is derived from his MAC address.

224
00:12:30,373 --> 00:12:33,206
For every interface ID that he has

225
00:12:35,089 --> 00:12:36,714
that's unique to him,
so right now he actually

226
00:12:36,714 --> 00:12:39,253
has two interface IDs, doesn't he?

227
00:12:39,253 --> 00:12:41,735
Actually if I derive it from his MAC,

228
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I actually probably should
have looked at his MAC

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and actually used that,

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so fe80::0211

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00:12:50,852 --> 00:12:52,185
:22ff:fe22:3333.

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00:12:56,887 --> 00:12:58,138
There we go.

233
00:12:58,138 --> 00:13:00,420
Okay, because this is actually
derived off of his real

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00:13:00,420 --> 00:13:02,062
MAC address right there.

235
00:13:02,062 --> 00:13:06,320
I just used EU 1/64 to come up with that.

236
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And just to make things
simple, let's just say that

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his global prefix is just like that too,

238
00:13:15,462 --> 00:13:16,545
0211:22ff:fe.

239
00:13:21,177 --> 00:13:23,177
I gotta do it over here.

240
00:13:27,586 --> 00:13:31,116
Okay, this makes it easy
because now we've used

241
00:13:31,116 --> 00:13:33,913
his MAC address in the
interface ID of both his global

242
00:13:33,913 --> 00:13:37,437
prefix as well as his Link-Local prefix.

243
00:13:37,437 --> 00:13:40,185
Okay, so every device does this.

244
00:13:40,185 --> 00:13:42,162
I'm just gonna focus on
the router for a moment,

245
00:13:42,162 --> 00:13:44,877
but then we'll see how the
laptop does this as well.

246
00:13:44,877 --> 00:13:49,148
So the router, once he comes
up with an interface ID,

247
00:13:49,148 --> 00:13:52,981
he also comes up with a
special address called

248
00:13:53,949 --> 00:13:57,403
a Solicited Node Multicast Address.

249
00:13:57,403 --> 00:14:00,150
And you can see here this one
is a nightmare to remember.

250
00:14:00,150 --> 00:14:02,638
Look how long and that
pattern, good luck with that.

251
00:14:02,638 --> 00:14:04,360
You're going to have to
memorize that pattern.

252
00:14:04,360 --> 00:14:08,342
But it's 104-bit pattern
that never changes,

253
00:14:08,342 --> 00:14:11,514
and the last 24-bits, 'cause
it has to be 128-bits,

254
00:14:11,514 --> 00:14:14,289
so the last 24-bits are actually taken

255
00:14:14,289 --> 00:14:17,247
from the interface ID itself.

256
00:14:17,247 --> 00:14:21,164
So based on this, here's
how he's gonna come up

257
00:14:22,584 --> 00:14:25,917
with a Solicited Node Multicast Address.

258
00:14:27,284 --> 00:14:29,016
I'm gonna get rid of the DHCP
Server so I have a little

259
00:14:29,016 --> 00:14:31,516
bit of room here at the right.

260
00:14:32,505 --> 00:14:34,043
And I'll put this in green to make it

261
00:14:34,043 --> 00:14:36,301
a little bit different.

262
00:14:36,301 --> 00:14:38,384
So it's gonna be ff02::1:

263
00:14:45,138 --> 00:14:46,805
so the last 24-bits.

264
00:14:48,306 --> 00:14:49,795
So let's see here, I'm
gonna put a red line

265
00:14:49,795 --> 00:14:52,976
under these last 24-bits
of the interface-ID.

266
00:14:52,976 --> 00:14:54,559
So there's 16-bits.

267
00:14:55,486 --> 00:14:56,403
There's 20.

268
00:14:57,297 --> 00:14:59,473
There's 24 right there.

269
00:14:59,473 --> 00:15:00,907
So those are the last 24-bits.

270
00:15:00,907 --> 00:15:02,758
'Cause remember it said right here,

271
00:15:02,758 --> 00:15:05,967
after this pattern right
here, the remaining 24-bits

272
00:15:05,967 --> 00:15:08,253
are taken from the interface-ID.

273
00:15:08,253 --> 00:15:10,014
So I've already started that pattern.

274
00:15:10,014 --> 00:15:11,090
I shortened my zeros.

275
00:15:11,090 --> 00:15:14,923
I used colon, colon for
the zeros right there.

276
00:15:15,937 --> 00:15:18,437
And I've got to put in the ff,

277
00:15:21,540 --> 00:15:25,207
and then the rest of
it I'll put it in blue.

278
00:15:27,566 --> 00:15:31,733
Okay so that is the Solicited
Node Multicast address.

279
00:15:38,411 --> 00:15:41,880
Now let's go over to this laptop here.

280
00:15:41,880 --> 00:15:45,130
He creates his IPv6 Link-Local address.

281
00:15:48,079 --> 00:15:50,261
So that's gonna be

282
00:15:50,261 --> 00:15:51,094
fe80::0211

283
00:15:55,453 --> 00:15:56,286
:33ff:

284
00:16:02,724 --> 00:16:03,557
fe33:4444.

285
00:16:06,714 --> 00:16:10,249
Okay, and I've already
explained how that's derived.

286
00:16:10,249 --> 00:16:14,332
Now he says, "Okay,
duplicate address detection."

287
00:16:15,440 --> 00:16:16,940
You know send out a neighbor solicitation

288
00:16:16,940 --> 00:16:19,030
making sure that nobody else has that.

289
00:16:19,030 --> 00:16:21,370
Great, nobody's got it.

290
00:16:21,370 --> 00:16:25,765
Then he says, "Okay,
now I need to send out

291
00:16:25,765 --> 00:16:27,765
"a router solicitation."

292
00:16:30,439 --> 00:16:32,939
So ICMPv6 Router Solicitation.

293
00:16:37,002 --> 00:16:39,670
Solicitation, yeah I got that right there.

294
00:16:39,670 --> 00:16:42,591
So the source is gonna be his

295
00:16:42,591 --> 00:16:43,508
fe80::0211:

296
00:16:48,881 --> 00:16:50,131
33ff:fe33:4444,

297
00:16:52,938 --> 00:16:54,820
I'm sort of running out of room here.

298
00:16:54,820 --> 00:16:58,637
And the destination will be
the all multicast router's

299
00:16:58,637 --> 00:17:00,054
address, ff02::2.

300
00:17:04,553 --> 00:17:07,422
So that is my router solicitation.

301
00:17:07,422 --> 00:17:10,628
The router gets that,
the router responds back.

302
00:17:10,628 --> 00:17:14,669
Now he uses his Link-Local
address as the source, fe80,

303
00:17:14,669 --> 00:17:16,455
responds back to this guy's
Link-Local and he says,

304
00:17:16,455 --> 00:17:19,788
"Hey, buddy, I'm using the 2001 prefix."

305
00:17:20,809 --> 00:17:23,873
So the laptop says, "Oh, okay,
great, then let me go ahead

306
00:17:23,873 --> 00:17:28,040
"and configure myself with
2001, and then I'll use

307
00:17:29,515 --> 00:17:33,682
"the exact same interface
ID that I did before, /64."

308
00:17:38,503 --> 00:17:42,253
He does duplicate address
detection for that.

309
00:17:43,242 --> 00:17:45,568
Now he says, let's put that little thought

310
00:17:45,568 --> 00:17:47,401
bubble in there again.

311
00:17:50,334 --> 00:17:52,417
He says, "I want to go to

312
00:17:54,113 --> 00:17:55,946
"the website at 2001",

313
00:17:58,752 --> 00:18:00,669
let's say 2004:4444::1.

314
00:18:05,481 --> 00:18:07,731
"That's NOT on my subnet!!"

315
00:18:10,647 --> 00:18:12,286
He says okay.

316
00:18:12,286 --> 00:18:14,456
The same thing as before.

317
00:18:14,456 --> 00:18:17,289
Right here he said, "Okay
when it's not on my subnet

318
00:18:17,289 --> 00:18:20,001
"I need to go to my router,
but hmm, didn't know

319
00:18:20,001 --> 00:18:21,359
"the MAC address of my router."

320
00:18:21,359 --> 00:18:22,339
So what did I do?

321
00:18:22,339 --> 00:18:24,677
In IP version four, I sent out a broadcast

322
00:18:24,677 --> 00:18:26,646
called an ARP Request.

323
00:18:26,646 --> 00:18:29,589
The router got it, sent
an ARP Response back

324
00:18:29,589 --> 00:18:31,112
and that's how I learned
about the MAC address

325
00:18:31,112 --> 00:18:32,426
of the router.

326
00:18:32,426 --> 00:18:34,176
In IPv6, we send out,

327
00:18:37,747 --> 00:18:38,580
and I don't know if I'm gonna have

328
00:18:38,580 --> 00:18:40,801
enough room here for this,

329
00:18:40,801 --> 00:18:43,468
an ICMPv6 Neighbor Solicitation.

330
00:18:47,250 --> 00:18:48,689
And so here we go.

331
00:18:48,689 --> 00:18:51,522
Source is gonna be his Link-Local,

332
00:18:55,268 --> 00:18:58,552
and the destination is gonna be

333
00:18:58,552 --> 00:19:02,719
the Solicited Mode Multicast
address of the router.

334
00:19:06,382 --> 00:19:10,903
Now you might be wondering
well, wait a second.

335
00:19:10,903 --> 00:19:15,070
Let me put this in a box here,
if I can squeeze it all in.

336
00:19:17,953 --> 00:19:20,402
You might be wondering
okay, I understand how when

337
00:19:20,402 --> 00:19:24,014
the PC sent the Neighbor Solicitation,

338
00:19:24,014 --> 00:19:26,679
I understand how he knew about this part

339
00:19:26,679 --> 00:19:28,649
because that's standard.

340
00:19:28,649 --> 00:19:30,914
Everybody knows about that.

341
00:19:30,914 --> 00:19:34,658
But how did he come up
with the last 24-bits?

342
00:19:34,658 --> 00:19:38,087
Well, remember when he sent
out a router solicitation

343
00:19:38,087 --> 00:19:40,428
to the all routers address

344
00:19:40,428 --> 00:19:43,678
and he got a router advertisement back?

345
00:19:44,783 --> 00:19:45,739
What was the source?

346
00:19:45,739 --> 00:19:47,328
So let me just write that
up here just to refresh

347
00:19:47,328 --> 00:19:48,328
your memory.

348
00:19:49,819 --> 00:19:53,402
Initially he sent out
a router solicitation

349
00:19:56,430 --> 00:19:59,180
to the all IPv6 router's address,

350
00:20:00,341 --> 00:20:04,008
and then he got back a
router advertisement.

351
00:20:06,750 --> 00:20:08,798
Now what did I say was the source

352
00:20:08,798 --> 00:20:11,710
of that router advertisement?

353
00:20:11,710 --> 00:20:14,951
I said it was the Link-Local
address of the router,

354
00:20:14,951 --> 00:20:15,868
fe80::0211,

355
00:20:19,192 --> 00:20:20,585
I'm kinda running out of room here,

356
00:20:20,585 --> 00:20:21,918
but it was this.

357
00:20:24,358 --> 00:20:28,434
Well remember how we said
the interface ID here

358
00:20:28,434 --> 00:20:32,500
was used to create the Solicited
Node Multicast address?

359
00:20:32,500 --> 00:20:36,358
So just like the router was
able to create that for himself

360
00:20:36,358 --> 00:20:40,905
the host, the PC said,
"Hmm, okay, I now know what

361
00:20:40,905 --> 00:20:44,246
"the router's Link-Local
address is because he responded

362
00:20:44,246 --> 00:20:48,300
"to me with a router
advertisement, so I know

363
00:20:48,300 --> 00:20:52,157
"that he is listening to a
Solicited Node Multicast address

364
00:20:52,157 --> 00:20:55,486
"that was derived from this,
and that's how he was able

365
00:20:55,486 --> 00:20:57,210
"to come up with that himself."

366
00:20:57,210 --> 00:21:00,081
As a matter of fact, the
laptop also had to create

367
00:21:00,081 --> 00:21:02,589
a Solicited Node Multicast address.

368
00:21:02,589 --> 00:21:04,848
I'll see if I can room up here to do that.

369
00:21:04,848 --> 00:21:09,542
So the laptop, he said,
"Alright, my Solicited Node,

370
00:21:09,542 --> 00:21:12,929
"just in case anybody
ever needs to resolve me

371
00:21:12,929 --> 00:21:16,179
"and figure out what my MAC address is,

372
00:21:18,143 --> 00:21:19,226
"is 33:4444."

373
00:21:24,216 --> 00:21:28,383
Remember it was the last 24-bits
after that static pattern,

374
00:21:30,503 --> 00:21:34,364
it was the last 24-bits
of the interface ID

375
00:21:34,364 --> 00:21:36,114
that was put in here.

376
00:21:37,731 --> 00:21:41,390
So every device comes up
with a Link-Local address

377
00:21:41,390 --> 00:21:45,473
for itself and a Solicited
Node Multicast address

378
00:21:46,650 --> 00:21:48,255
for itself.

379
00:21:48,255 --> 00:21:50,675
And if anybody every needs to ARP for it,

380
00:21:50,675 --> 00:21:53,045
well, there is no ARP
in the world of IPv6,

381
00:21:53,045 --> 00:21:55,962
but there is Neighbor Solicitation,

382
00:21:56,863 --> 00:21:59,248
and they will send a Neighbor Solicitation

383
00:21:59,248 --> 00:22:02,581
to your Solicited Node Multicast address

384
00:22:03,603 --> 00:22:05,571
which is what you're listening for.

385
00:22:05,571 --> 00:22:07,997
And then the router in
turn will respond back,

386
00:22:07,997 --> 00:22:10,330
and this is the final piece,

387
00:22:11,524 --> 00:22:16,082
he'll respond back with
a neighbor advertisement,

388
00:22:16,082 --> 00:22:18,582
ICMPv6 Neighbor Advertisement,

389
00:22:25,407 --> 00:22:28,237
and that is how this PC will
learn of the MAC address

390
00:22:28,237 --> 00:22:29,925
of the router.

391
00:22:29,925 --> 00:22:32,924
So to recap in the
world of IP version four

392
00:22:32,924 --> 00:22:35,788
to learn someone's MAC address
who is on your same wire,

393
00:22:35,788 --> 00:22:38,541
you sent out an ARP
Request and you got back

394
00:22:38,541 --> 00:22:40,306
and ARP Response.

395
00:22:40,306 --> 00:22:44,866
In the world of IPv6, you send
out a Neighbor Solicitation

396
00:22:44,866 --> 00:22:48,279
and you get a Neighbor Advertisement back.

397
00:22:48,279 --> 00:22:51,810
In the world of IP version
four, a lot of protocols

398
00:22:51,810 --> 00:22:53,060
use broadcasts.

399
00:22:54,024 --> 00:22:58,498
In the world of IP version
six, there is no broadcast.

400
00:22:58,498 --> 00:23:03,225
If you absolutely must talk to
everybody who is on your wire

401
00:23:03,225 --> 00:23:06,837
you send a packet to this address,

402
00:23:06,837 --> 00:23:09,212
the all IPv6 nodes address.

403
00:23:09,212 --> 00:23:12,326
That's basically the
equivalent of a broadcast.

404
00:23:12,326 --> 00:23:15,779
Even though it's a multicast,
everybody's listening to it,

405
00:23:15,779 --> 00:23:19,041
but usually we don't send stuff to that.

406
00:23:19,041 --> 00:23:21,666
We send stuff either to
the all routers address

407
00:23:21,666 --> 00:23:24,821
or we send it to their
Solicited Node Multicast address

408
00:23:24,821 --> 00:23:27,118
or to their Link-Local address.

409
00:23:27,118 --> 00:23:30,729
So I know there's a lot
of addresses here in IPv6,

410
00:23:30,729 --> 00:23:32,155
and that's just something
you're gonna have to go over

411
00:23:32,155 --> 00:23:35,238
and over and over again to memorize.