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[AUDIO LOGO]

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So let's begin our discussion on
tunneling by talking about some

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of our manual tunneling choices.

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That would be specifically
GRE tunnels and 6in4 tunnels.

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Now, these are very similar.

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The main difference,
as we'll see

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as we go through
this video, is what

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the headers are on the packets.

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Essentially, how it's
encapsulated for the tunnel.

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There's a slight
difference there,

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and that's one of the
things we need to discuss.

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But what do we mean
by manual tunnels?

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Well, quite simply, we
mean that not only do we

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have to configure all of the
attributes of the tunnel,

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which, of course,
would be normal,

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but when it comes to the
tunnel source and destination,

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we are going to have
to specify both.

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We'll see in some
upcoming videos

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when it comes to
automatic tunnels,

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the destination
for that tunnel is

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going to be learned
some automatic way.

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Now, there's different
ways for that to happen,

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and we need to discuss that.

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But these are going to
be manual tunnels, which

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means we, as administrators,
are going to be configuring

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not only the source, but also
the destination for the tunnel.

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That makes these pretty much
just point-to-point tunnels.

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And of course,
our main goal here

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is going to be to support
IPv6 over the tunnel and IPv4

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as the underlying transport.

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So let's go ahead and
jump in and take a look

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at some of these details
about the manual tunnels,

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and of course, a
little bit about what's

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the difference between a GRE
tunnel and a 6-in-4 tunnel.

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So let's go ahead and take
a look at those details.

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So as we basically
mentioned, the idea

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behind tunneling
itself is that we

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want to connect
these islands of IPv6

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over a network or
a transit network

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that only supports IPv4.

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That's the main reason
we're doing this.

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If we were doing dual stack,
like we discussed previously,

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we wouldn't need tunneling.

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So let's talk about
the requirements

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in order to do this tunneling.

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First, let's talk about the
underlay or the underlying

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network, which is IPv4.

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What we need to have is
reachability, specifically

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for those tunnel endpoints.

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Remember, the IPv6 itself
is going to be encapsulated.

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Therefore, the underlay
network doesn't

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have to know anything
about the IPv6.

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It will never see
this IPv6 that's

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just going over the tunnel.

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So what we care about is simply
reaching these endpoints.

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That's really all we need from
the underlying IPv4 network.

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Now, as we have
mentioned previously,

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those endpoints are going
to have to be dual stacked.

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The IPv6 is going to be used
for the connected networks

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or again, those
islands that we're

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trying to connect over the IPv4
network, and of course, running

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over the tunnel itself
to connect those islands

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of IPv6 networks.

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IPv4 is simply used for
the underlay network

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or the transport network.

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Now, there are a few or
many different tunneling

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protocols which can
handle IPv6 over IPv4.

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Some of these are manual.

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And of course, that's
what we're going

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to be discussing in this video.

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And some of those are automatic.

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And we'll be talking about
those in upcoming videos.

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And just a quick note here, when
we say there are many tunneling

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mechanisms, we're
going to be talking

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about the ones primarily used
in a service provider core.

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Keep in mind, there's
other tunnel types

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such as ISATAP tunnels.

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We also have Teredo tunnels.

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So there are different
tunnels available for IPv6

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that are a little beyond
the scope of this course

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because they're not really
focused on service provider.

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But there are other types
of tunnels out there even

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beyond what we're going
to be discussing here.

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So as we mentioned,
the two tunneling types

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that we're going to be
discussing in this video

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are both manual options.

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And again, what that means
is that both the source

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and the destination of the
tunnel must be configured.

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And again, this would
be by the administrator.

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So that's what really
makes these manual tunnels.

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So the first one we want to
discuss is the GRE tunnel.

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Now, again, GRE stands for
Generic Routing Encapsulation.

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This is a tunneling
protocol that was actually

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developed by Cisco
a long time ago,

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and its main job is to be able
to carry multiple protocols

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over another protocol.

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Now, these are generally going
to be point-to-point tunnels.

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Although, we certainly
have multipoint

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GRE tunnels for other
technologies such as DMVPN.

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So again, not
something we're going

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to get into in this course.

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But just be aware that GRE
is not necessarily always

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point-to-point, but it
is for this discussion.

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Just as a quick note,
DMVPN is not really

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one of our discussions
in this course

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simply because it's more of
a customer side technology.

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However, just as a quick note,
it supports IPv6 as well.

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So that is another
tunneling option.

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Now, at the end of the day,
it's still using GRE headers.

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So it falls under
this same umbrella.

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It's just that it's
multipoint and automatic

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but still using the
GRE encapsulation.

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So back to some more
detail on GRE itself,

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this is transported directly
on top of IP as protocol 47.

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This means that there is no
TCP header or UDP header that's

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used in this environment.

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The GRE headers come directly
after the IP headers.

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Now, this does add
a 4-byte header,

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and this is in addition to
the new outer IP header.

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Remember that the IP
header is 20 bytes.

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We need this header
because it's a tunnel.

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So we're going to be putting
a standard IPv4 header

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in front of either the GRE
header or the IPv6 header.

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This means that for
GRE, we are picking up

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an additional 24 bytes of
overhead over the IPv6 packet

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by itself.

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That's the cost of the tunnel
or the tunneling overhead.

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Now, IPv6 can be enabled on
a GRE tunnel, in addition

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to other protocols such as IPv6
4 because of this GRE header.

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The GRE header, which is that
4 bytes, has a protocol header.

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The protocol header tells
it what the payload is.

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The reason that's
important is, this header

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is what allows that tunnel
to carry multiple protocols

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at the same time.

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It can support IPv4
and IPv6 simultaneously

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on the same tunnel.

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The reason we're
bringing this up

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now is simply to contrast
this to 6in4 tunnels

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that we're going to talk
about in just a moment.

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So now, let's jump
in and take a look

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at how we configure these
tunnels on both IOS XR and IOS

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XE.

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So starting with IOS
XR, all we have to do

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is create an
interface, specifically

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the interface type is
going to be tunnel-ip.

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We, of course, give it a number.

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Then, we specify an IPv6
address for the tunnel itself.

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We set the tunnel mode
to be GRE over IPv4.

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We then set the tunnel source
and the tunnel destination.

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One quick note as we're going
over configurations here,

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I'm only showing
configuration related

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to the exact tunnel
or technology

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that we're talking
about at the moment.

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Keep in mind that everything
else involved in this

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would have to be configured.

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We would have to have
routing protocols,

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other interfaces
configured, and so on.

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This is just focusing on
the tunnel configuration

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itself just so we're clear.

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That's going to apply for
the whole rest of the skill.

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Now, we're going to see that IOS
XE's configuration is actually

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very similar.

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We, again, create a
tunnel, but this time, we

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don't have to say tunnel-ip.

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We just say interface tunnel.

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We, again, give it
an IPv6 address.

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We say tunnel mode gre.

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Now, you can say
tunnel mode gre ip,

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or you can leave this
command out completely.

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Notice, I have a little
note there that this

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is the default, which
means, you don't actually

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have to put that
command in at all.

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That is the default
operational mode on IOS XE.

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We, again, specify the
tunnel source and the tunnel

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destination.

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And just as a reminder,
through our routing protocols

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and the underlay network,
the tunnel source,

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whatever that is, in
this case, a loopback,

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has to be able to reach whatever
the destination address is.

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So what makes 6-in-4
tunnels different.

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Well, the main difference
is that this carries

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the IPv6 header
directly on top of,

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or you could say directly
behind the IPv4 header.

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There is no GRE header.

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So the GRE header is
gone in this case.

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And ultimately,
what that means is,

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it means we're going to save
those 4 bytes of overhead that

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were taken up by the GRE header.

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Now, that's not a
lot, but if we're

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talking about millions
and millions of packets,

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that can certainly add up
as far as the overhead.

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Now, of course, the
downside of this

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is, since we no longer
have the GRE header

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to identify that protocol field,
that means that this can only

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carry one protocol because
there's no GRE header to say,

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is this IPv4?

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or is this IPv6?

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when a packet arrives
at the receiving end.

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And that also means
that both sides

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are going to have
to be configured

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to be a 6-in-4 tunnel.

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Both sides have to understand
that the packets coming

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through this tunnel are going
to be IPv6 because again, there

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is no protocol field to tell
them which protocol it is.

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So they just have to be
configured appropriately.

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The way we do that
configuration,

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notice that on IOS XR.

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The only thing that's different
here is the tunnel mode.

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It's an IPv4 tunnel.

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On IOS XE, we simply change
the mode, and it's IPv6 IP.

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So this is how we
configure our GRE tunnels

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and our 6-in-4 tunnels
on IOS XR and IOS XE.

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So in this video, we saw how
to configure manual tunnels,

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specifically GRE
and 6-in-4 tunnels

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between our different devices
over an IPv4-only network.

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This, again, allows us to
connect islands of IPv6

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without the transport network
having to know anything

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about IPv6 at all.

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Now, again, the
big thing here is

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we have to configure both the
source and destination, making

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this a point-to-point
manual tunnel.

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Now, the obvious problem with
this from a service provider's

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perspective, this isn't
going to scale very well.

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We have thousands, if not,
millions of customers.

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We sure as heck can't
build these tunnels

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for all those customers.

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So a lot of times, we're
going to need a more automatic

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solution, and
that's exactly what

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we're going to look at next.

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We're going to jump
in and start looking

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at some of the various
automatic options.

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Until 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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