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[AUDIO LOGO]

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Now that we have our
tunnel up and running

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and we've talked about
the different protocols

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and signaling that have to
happen for that to work,

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now it's time to actually get
traffic to go down the tunnel.

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We call this traffic steering
because we're steering traffic

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into the tunnel.

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Now, there's a few
ways we can do that.

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And that's what we want to
talk about in this video.

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So there's three
major ways to do it.

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Let's just go ahead and
jump in and take a look

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at each of those three methods.

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So the term traffic
steering simply

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refers to routing or forwarding
the traffic into the TE tunnel

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that we've previously
established.

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Just establishing the tunnel
does not cause the traffic

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to go down that tunnel.

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We have to actually force the
traffic or route the traffic

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into said tunnel.

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Now, there are a
few ways to do this.

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We're going to be looking
at three specifically.

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The first is static routes.

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Second is policy-based routing.

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And the third is the
autoroute feature.

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So let's look at
these one by one

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and talk about some advantages
and disadvantages of each.

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So for the static routing
option, the first one up there,

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we're going to list
the destination network

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that we're trying to get to.

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And the way this
gets configured is

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the next hop is going to be
the far end of the tunnel.

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That's how we configure
the static route.

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The egress interface from
the router's perspective

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will be the tunnel
interface itself.

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Remember, the tunnel
is an interface.

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It's not an
interface to the IGP.

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But it is still an interface.

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So when we set up
our static route,

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the egress interface
will be that tunnel.

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Now, for much the same reason
we don't use static routing

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in most of our networking,
the big downside

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here is this, of course,
does not scale well at all.

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And as we've
already established,

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scalability is rather
important in a service provider

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environment.

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Now, I didn't put an
actual section in here

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for the policy-based
routing option,

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because at the end of the
day, for this discussion,

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policy-based routing
is pretty much the same

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as static routing.

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In other words, we're
going to set the next hop

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to the far end of the tunnel.

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The egress interface
would be the tunnel.

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And again, this also
does not scale well.

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So for the sake of
this discussion,

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static routes and
policy-based routing

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can pretty much be
grouped together

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into the same category.

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The better option is
the autoroute feature,

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again unless you have
a particular reason

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to use one of the other choices.

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So how does this
feature actually work?

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Well, first off, the
head-end router and only the

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head-end router, which is
what we're saying down here.

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Again, it only affects
the head-end router.

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But it sees the TE tunnel as a
directly connected interface.

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So as we've said, this is an
interface, just not in the IGP.

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So again, this tunnel will be
used for the normal IGP route

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calculation but not for our
constraint-based routing.

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Again, it doesn't get considered
in the actual calculation

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for creating the tunnel.

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But since it is considered in
our normal IGP calculation,

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any prefixes at the
far end of that tunnel

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or behind that tunnel will
then be routed down the tunnel.

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Now, this is, of
course, assuming

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that the metrics are correct.

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So now we have to talk
about autoroute metrics.

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Remember that the idea here is
we want the tunnel to be used.

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That's why we're building it.

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So by default, that
tunnel is going

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to be given the best IGP
metric to the tunnel endpoint.

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This allows it to be compared
to the underlying metric.

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And if there are
equal tunnels, they

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can actually be load balanced.

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Now, remember we said before
that the tunnel will not

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load balance.

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But that's not what
we're talking about here.

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Here we're talking about
having two separate tunnels

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with the same destinations
behind those tunnels.

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Therefore, it will load
balance between the tunnels.

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That's just, again,
doing standard IGP

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equal-cost multipathing.

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It's just that
the tunnels happen

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to be the egress interfaces.

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Now, just be aware that
this default behavior can

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cause issues if the
tunnels are following

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the same physical path.

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The reason for
this, of course, is

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because the IGP thinks it's
doing equal-cost multipathing.

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But it's actually going
down the same physical path.

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The way we get around
this is by ensuring

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that the tunnels follow
different physical paths

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by adjusting the metrics to
make sure that they're not

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following that path.

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And we have two choices
when doing this.

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They can either be relative
metrics to each other.

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Or just configure
absolute metrics.

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And that's really up
to a design choice

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by the network administrator.

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So in this video, we
saw different ways

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of getting traffic to
go into the tunnel.

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We looked at static.

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We talked about
PBR, or Policy-Based

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Routing, and of course,
the autoroute feature.

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As you can probably guess,
the autoroute feature

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is generally preferred
because we're using our IGP

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to route the traffic.

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And we all know why we
like to use IGPs as opposed

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to static or
policy-based routing.

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But we do have the
option to do those

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if you need that
level of control.

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So that concludes everything we
need to discuss in this skill.

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In our next skill,
we'll actually

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be jumping onto the command
line and putting all of this

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to work.

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Until then, we're
going to wrap up

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with a review in
the form of a quiz.

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And that's exactly what
we're going to do next.

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Until then, 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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