[MUSIC PLAYING]
In this video, let's jump in and take a look at that first rule
that we prefer internal over external routes.
This is going to be a fairly easy rule to prove.
So we'll start off by looking at our topology,
just to talk about what we're going to be building.
And then we're going to jump onto the command line
and see this first rule in action.
Let's get started.
So in order to compare our internal to external routes,
what we're going to do is, first we will take a look at this
external route which we're going to be focusing on a loopback
that's currently on router 10 that has an address
of 100.100.100.0.
And this is a /24.
So this is going to be the main route we're going to focus on.
We're going to start by looking at this on router 7.
And then we're going to create an internal version
of that same route.
But we're going to put a high cost on it.
So in other words, we're going to make it
so the external route should be chosen, theoretically, if it
was going to come down to cost.
That way, we can make sure that it's not coming down to cost.
We will create that new loopback on router 8.
And we'll then bring that into OSPF area zero
so that it's an internal route.
And we will of course, see what that does as far as our path
selection.
So let's go ahead and get started.
Again, we'll start on router 7 just examining and making
sure we have that external route from router 10.
So we'll start by looking at that prefix to 100.100.100.0.
/24.
And what we see is we are, in fact, learning this
from an external type 2.
Its current metric is 20.
And it is in fact using a next hop of 50.1.167.6,
which it learned from router 10.
So this is clearly using that external route
from router 10 coming through the ABR of router 6.
So now let's see what happens if we bring this
in as an internal route.
We'll do that on router 8.
So here, we'll simply make an interface loopback 100.
We'll give it an IP address on the 100.100.100.0/24.
We'll make this a .8.
Again, it's a /24.
Now we do have to make this OSPF network type point-to-point
because the default for a loopback,
is, well, type loopback.
And that would make it advertise it as a /32.
In order for this to be identical to that external
route, it's going to have to be a /24.
So we'll change this here to point-to-point.
We'll bring it into our area 0.
And we'll give it a very high cost,
which means that this, theoretically if it was just
lowest cost wins, this would in no way
beat out that external with a metric of 20.
But let's go see what's happening over on router 7.
If we come back here to router 7, we look at our route again.
And what we see is we now have an intra area, clearly
internal, and it's still using that really high metric
of 1001.
So even though clearly the metric of 20 on our external
would have been a lower cost, we see that that's not
what made the decision here.
The decision came down to internal beats external.
In this video, we just did a quick demonstration
that regardless of lowest cost, it
doesn't matter if one route is internal and one is external.
That internal route will always win.
I hope this has been informative for you.
And I'd like to thank you for viewing.