[AUDIO LOGO]
Now that we have our tunnel up and running
and we've talked about the different protocols
and signaling that have to happen for that to work,
now it's time to actually get traffic to go down the tunnel.
We call this traffic steering because we're steering traffic
into the tunnel.
Now, there's a few ways we can do that.
And that's what we want to talk about in this video.
So there's three major ways to do it.
Let's just go ahead and jump in and take a look
at each of those three methods.
So the term traffic steering simply
refers to routing or forwarding the traffic into the TE tunnel
that we've previously established.
Just establishing the tunnel does not cause the traffic
to go down that tunnel.
We have to actually force the traffic or route the traffic
into said tunnel.
Now, there are a few ways to do this.
We're going to be looking at three specifically.
The first is static routes.
Second is policy-based routing.
And the third is the autoroute feature.
So let's look at these one by one
and talk about some advantages and disadvantages of each.
So for the static routing option, the first one up there,
we're going to list the destination network
that we're trying to get to.
And the way this gets configured is
the next hop is going to be the far end of the tunnel.
That's how we configure the static route.
The egress interface from the router's perspective
will be the tunnel interface itself.
Remember, the tunnel is an interface.
It's not an interface to the IGP.
But it is still an interface.
So when we set up our static route,
the egress interface will be that tunnel.
Now, for much the same reason we don't use static routing
in most of our networking, the big downside
here is this, of course, does not scale well at all.
And as we've already established,
scalability is rather important in a service provider
environment.
Now, I didn't put an actual section in here
for the policy-based routing option,
because at the end of the day, for this discussion,
policy-based routing is pretty much the same
as static routing.
In other words, we're going to set the next hop
to the far end of the tunnel.
The egress interface would be the tunnel.
And again, this also does not scale well.
So for the sake of this discussion,
static routes and policy-based routing
can pretty much be grouped together
into the same category.
The better option is the autoroute feature,
again unless you have a particular reason
to use one of the other choices.
So how does this feature actually work?
Well, first off, the head-end router and only the
head-end router, which is what we're saying down here.
Again, it only affects the head-end router.
But it sees the TE tunnel as a directly connected interface.
So as we've said, this is an interface, just not in the IGP.
So again, this tunnel will be used for the normal IGP route
calculation but not for our constraint-based routing.
Again, it doesn't get considered in the actual calculation
for creating the tunnel.
But since it is considered in our normal IGP calculation,
any prefixes at the far end of that tunnel
or behind that tunnel will then be routed down the tunnel.
Now, this is, of course, assuming
that the metrics are correct.
So now we have to talk about autoroute metrics.
Remember that the idea here is we want the tunnel to be used.
That's why we're building it.
So by default, that tunnel is going
to be given the best IGP metric to the tunnel endpoint.
This allows it to be compared to the underlying metric.
And if there are equal tunnels, they
can actually be load balanced.
Now, remember we said before that the tunnel will not
load balance.
But that's not what we're talking about here.
Here we're talking about having two separate tunnels
with the same destinations behind those tunnels.
Therefore, it will load balance between the tunnels.
That's just, again, doing standard IGP
equal-cost multipathing.
It's just that the tunnels happen
to be the egress interfaces.
Now, just be aware that this default behavior can
cause issues if the tunnels are following
the same physical path.
The reason for this, of course, is
because the IGP thinks it's doing equal-cost multipathing.
But it's actually going down the same physical path.
The way we get around this is by ensuring
that the tunnels follow different physical paths
by adjusting the metrics to make sure that they're not
following that path.
And we have two choices when doing this.
They can either be relative metrics to each other.
Or just configure absolute metrics.
And that's really up to a design choice
by the network administrator.
So in this video, we saw different ways
of getting traffic to go into the tunnel.
We looked at static.
We talked about PBR, or Policy-Based
Routing, and of course, the autoroute feature.
As you can probably guess, the autoroute feature
is generally preferred because we're using our IGP
to route the traffic.
And we all know why we like to use IGPs as opposed
to static or policy-based routing.
But we do have the option to do those
if you need that level of control.
So that concludes everything we need to discuss in this skill.
In our next skill, we'll actually
be jumping onto the command line and putting all of this
to work.
Until then, we're going to wrap up
with a review in the form of a quiz.
And that's exactly what we're going to do next.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.