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- You have just learned
how to work with IPv4.

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And in most cases, IPv4
is what you will be using.

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But it's a fact that the world

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is running out of IPv4 addresses.

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And that is why there
is a next version of IP,

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and that's IPv6.

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In case you are wondering
what happened to IPv5,

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well, it was proposed one
day, but it never made it.

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So we skipped IPv5.

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Nobody ever heard about it anymore.

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In IPv6, 128 bits is used

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to write the addresses,

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and the addresses are
written in a hexadecimal way.

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Hexadecimal is a numbering
system from 0 up to 15.

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And in order to use that numbering system,

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we use the number zero up to nine,

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and then a, b, c, d, e, and
f as the additional numbers.

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And that makes it what we see right here.

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It's a valid IPv6 address.

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As you can see, these are
not so easy to work with.

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In an IPv6 address, you
can omit leading zeros,

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as well as long string of zeros.

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So fe80::1 is a valid address.

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That just means that the
address starts with fe80,

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and then, there's a whole lot of zeros

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and it ends with a one.

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Fortunately, you can
summarize the IPv6 addresses

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to make it a little bit more manageable.

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When you are referring to an
address followed by the port,

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then you need to put the
address between square brackets,

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as in this example

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where you can see port 80 on fe80::1.

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And it's quite obvious why
you need the square brackets.

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That is because the colon has a meaning

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in a network socket.

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In a network socket,

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which consists of IP
address followed by port,

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the colon is normally used as a separator.

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But in IPv6, the colon is
also used as a separator.

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Well, to avoid any confusion,
we have the square brackets.

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In IPv6, we have a default subnet mask.

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The subnet mask distinguish
between the part of the address

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that is used as the network address

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and the part that is
used as the node address.

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And by default, the subnet mask is /64.

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So the first half is for the network,

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the second half is for the node.

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And the node bit of the address

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may contain the device MAC address.

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And that's because IPv6
has this nice solution

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to automatically assign IP addresses.

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Now, in IPv6, there's a
couple of IP addresses

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that are reserved.

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Let's talk about those.

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To start with, there is ::1,

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which is the equivalent to IPv4 127001.

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That's a localhost IP address.

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There is ::, which is
the unspecified address,

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000 in IPv4.

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And ::/0 refers to the default route.

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And then there is a couple of addresses

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that are reserved as well.

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Anything starting with
2000 and a subnet mask /3

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is what we call the
global unicast address.

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The global unicast address

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is a worldwide unique address

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that can be used on the Internet.

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And the IPv6, folks, have
done something smart.

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And that is, they have reserved

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a couple of IPv6 addresses only.

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Anything starting with 2000/3.

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And that means that a
lot of IPv6 addresses

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are not used at all at the moment.

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They are for future use.

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And we can do that because in IPv6,

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given the 128 bits address space,

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you can use an incredible
lot of IPv6 addresses.

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To be precise,

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4 billion times 4 billion times
4 billion times 4 billion.

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You try to pronounce the result of that.

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I don't know how to pronounce it.

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Back to the reserved IPv6
addresses, there is fd00.

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These are unique local
addresses or private addresses.

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And these private addresses
can be used for internal use.

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So it's a little bit like 192 168 in IPv4.

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Then we have fe80.

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fe80 is for link-local addresses.

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And link-local addresses

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are addresses that are
automatically assigned.

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You don't have to assign them yourself.

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These are addresses that
are created automatically

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based on the MAC address

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that was found on your network interface.

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And because these IPv6 addresses

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are created automatically,

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you get the default IPv6
functionality within your network,

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and that's convenient.

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And finally, there is ff00,
which is a multicast address.

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Now, how do we get an IPv6 address?

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Well, you will notice that interfaces,

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by default have an fe80 address.

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You can also do a static addressing.

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That is where you are going
to assign them yourselves.

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And you can use DHCPv6.

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Now, in DHCPv6, the IPv6 client

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sends out a multicast address to ff02::1:2

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on port 547.

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That is the all-DHCP multicast group.

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And if the DHCP server is
listening, it will answer.

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The other option is stateless
address auto configuration.

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Now, how does that work?

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Well, the IPv6 client

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is sending a so-called router solicitation

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to the multicast address ff02:2.

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And that is the all-routers
multicast group.

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And if there's a router that
is configured with IPv6,

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then it will answer
back with its IP address

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that allows the host to
learn the network prefix,

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and it will automatically
create its own IP address

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by creating the node port

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based on the MAC address
of that network card.

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Sounds a little bit complicated,

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but in fact, it's really simple.

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You have a node that
needs an IPv6 address,

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it is going to come up,

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it sends a message over the network,

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and its message is like,

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"Hey, is there a router that can help me?"

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And if there is a router that can help,

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the router will answer.

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And in the answer,

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the requesting node will
learn the network IP address

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and it's assigning its own node ID to it,

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and you have an automatically
created IPv6 address.

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The only requirement

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is that you need a stateless
address auto configuration

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compatible router.

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On Linux, you can create such a router

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by installing radvd
package on the Linux node.

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But Linux is not used commonly as a router

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so you probably have a Cisco router

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or something else taking care of this.