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[AUDIO LOGO]

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So now, let's take
our first look

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at an automatic
IPv6 over IP tunnel.

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Specifically, we're going to
look at 6to4 automatic tunnels.

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Now, an automatic
tunnel simply means

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that the tunnel
is going to learn

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the destination on its own,
but that does beg a question.

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How is it going to do that?

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Well, that's what
we have to answer.

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How does the tunnel learn
the IPv4 destination

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that it needs to
build the tunnel for?

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So that's going to be our
primary conversation because

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besides that, well, this is
essentially a 6in4 tunnel.

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So let's go ahead and jump
in and talk about some

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of the details on how
this works specifically

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for our 6to4 automatic tunnels.

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So as we mentioned,
6to4 tunneling

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is an automatic
tunneling method.

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So let's talk a bit about
how this actually functions.

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First thing, we did mention
this during the introduction.

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This is still using
6in4 encapsulation,

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which simply means that,
again, the IPv6 header is

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coming directly behind
the IPv4 header.

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This does not use GRE headers.

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It's also very important to
note that this uses the reserved

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address space of 2002::/16.

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This is by definition,
and it's not an option.

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So any time we see this
2002 address space,

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we should be pretty
sure that this

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is being used for a
6to4 tunnel, or well,

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somebody using it incorrectly.

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Then what we do is,
each site is then

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going to be given
an IPv6/48 prefix.

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Now, this /48 prefix is going
to be based on the IPv4 tunnel

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endpoint address.

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Keep in mind, of
course, IPv4 is 32-bit.

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So when we add the 32 bits
to the end of the /16,

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that's where that /48 comes from
that we're going to be giving

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to that remote site.

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Now, if that other site has
the need to subnet further,

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keep in mind that we can
subnet that /48 maybe to a /64,

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something along those lines,
just as we would with any other

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IPv6 prefix.

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But ultimately, how
does all of this help?

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Well, this is the key
factor right here,

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when a packet arrives on
this tunnel interface.

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Now, this isn't really part
of our discussion right now,

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but how would it know to arrive
at this tunnel interface?

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Well, that's where the
routing comes into play.

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We're not focusing on the
IPv6 routing right now.

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But again, it's going to be
from the routing protocols.

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The packet arrives
at this tunnel.

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And then we extract
the IPv4 address

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of the tunnel destination.

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We're pulling that out of
this /48 prefix and using that

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to then build the tunnel.

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So this is the
fundamental principle

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behind how the
6to4 tunnels work.

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So let's take a look at an
example of the addressing

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and how we would configure this.

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So first, let's take
a look at an example.

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So we're given an IPv4
address of a tunnel endpoint

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and what the IPv6
prefix would look like.

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So here's how this
ultimately works.

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First, we have the part
of the address that's

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a given, which is the 2002.

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Then the 210 is going to be
converted to this d2 right

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here.

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The 112 is going to be
converted to this 70 right here.

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The 35 gets converted
to the 23, and the 80

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gets converted to the 50.

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And of course, by
converted, we simply

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mean we're converting
the decimal into hex.

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This is how this becomes a
/48, and this is what gets

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configured when we
set up our devices.

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So to go over this, we, again,
create an interface tunnel 100,

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but notice the IPv6
address for the tunnel.

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So this is how we
would configure

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this particular tunnel.

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We would give it the address,
and we configure it above.

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We would set up
our tunnel source,

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and we set the tunnel
mode to be IPv6 IP,

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and then we add
this keyword 6to4.

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That's what tells it to
look for this 2002 address

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and extract the IPv4
address from it.

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Then, of course, we're
going to need a route

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to send the traffic
down this tunnel.

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Now, it could be more specific.

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But in most cases,
since the 2002

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is dedicated for
6to4 tunnels anyway,

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we usually just route the entire
address space down the tunnel.

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So in this case, we're
routing it down tunnel 100.

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So ultimately, 6to4
tunnels work very well.

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However, not everything
is without drawbacks,

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and this does have
some drawbacks.

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So let's go ahead
and take a look.

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So the drawbacks of
the 6to4 tunnels,

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the first one may already be a
little bit obvious and that it

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does require the use of that
reserved IPv6 address space,

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the 2002::/16.

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Now, normally speaking,
that may not matter.

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However, this can definitely
create a problem down the road

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when you're getting
rid of tunnels,

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and you're actually going to
switch over to native IPv6.

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Because if we're
on native IPv6, we

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should no longer be using
that reserved address space.

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We should be using normal
IPv6 address space.

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So that's our first drawback.

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Another drawback is what if
that IPv4 address of the site

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changes.

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That means that the IPv6
prefix for that site

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would have to change
as well, and that

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may take some manual
intervention to get that tunnel

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to function properly again.

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And if we're going to
provide our customers

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with internet access
using this solution,

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this is going to
require a 6to4 relay

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router that we have to
make available for them

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to step this traffic
off to the internet.

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But these few drawbacks
aside, 6to4 automatic tunnels

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are actually a
really good solution

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for automatically configuring
tunnels to send IPv6 over IPv4.

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So in this video, we took a
look at automatic IPv6 tunnels,

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specifically 6to4 tunnels.

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These, of course, require the
use of the 2002::/16 reserved

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address space.

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Again, if all of this
is for tunneling,

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that's really not a big deal.

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But hopefully, the
plan is to migrate away

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from tunnels at some
point and run native IPv6.

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And if that's the
case, well, we wouldn't

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want to be using these reserved
address spaces anymore.

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So what would be
ideal would be to have

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all the advantages of 6to4
tunnels, meaning they're

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automatic and being able to
use whatever address space

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we want and assign that
to the customers so

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that they could
use that long term.

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Well, we actually have
a solution for that,

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and we're going to
look at it next.

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Till then.

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I hope this has been
informative for you,

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and I'd like to thank
you for viewing.

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