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[MUSIC PLAYING]

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In this video, let's jump in and
take a look at that first rule

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that we prefer internal
over external routes.

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This is going to be a
fairly easy rule to prove.

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So we'll start off by
looking at our topology,

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just to talk about what
we're going to be building.

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And then we're going to
jump onto the command line

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and see this first
rule in action.

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Let's get started.

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So in order to compare our
internal to external routes,

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what we're going to do is, first
we will take a look at this

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external route which we're going
to be focusing on a loopback

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that's currently on router
10 that has an address

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of 100.100.100.0.

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And this is a /24.

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So this is going to be the main
route we're going to focus on.

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We're going to start by
looking at this on router 7.

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And then we're going to
create an internal version

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of that same route.

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But we're going to
put a high cost on it.

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So in other words,
we're going to make it

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so the external route should
be chosen, theoretically, if it

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was going to come down to cost.

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That way, we can make sure that
it's not coming down to cost.

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We will create that new
loopback on router 8.

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And we'll then bring
that into OSPF area zero

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so that it's an internal route.

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And we will of course, see what
that does as far as our path

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selection.

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So let's go ahead
and get started.

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Again, we'll start on router
7 just examining and making

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sure we have that external
route from router 10.

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So we'll start by looking at
that prefix to 100.100.100.0.

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/24.

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And what we see is we are,
in fact, learning this

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from an external type 2.

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Its current metric is 20.

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And it is in fact using
a next hop of 50.1.167.6,

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which it learned from router 10.

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So this is clearly using
that external route

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from router 10 coming
through the ABR of router 6.

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So now let's see what
happens if we bring this

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in as an internal route.

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We'll do that on router 8.

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So here, we'll simply make
an interface loopback 100.

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We'll give it an IP address
on the 100.100.100.0/24.

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We'll make this a .8.

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Again, it's a /24.

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Now we do have to make this
OSPF network type point-to-point

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because the default
for a loopback,

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is, well, type loopback.

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And that would make it
advertise it as a /32.

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In order for this to be
identical to that external

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route, it's going
to have to be a /24.

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So we'll change this
here to point-to-point.

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We'll bring it into our area 0.

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And we'll give it
a very high cost,

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which means that this,
theoretically if it was just

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lowest cost wins,
this would in no way

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beat out that external
with a metric of 20.

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But let's go see what's
happening over on router 7.

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If we come back here to router
7, we look at our route again.

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And what we see is we now
have an intra area, clearly

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internal, and it's still
using that really high metric

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of 1001.

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So even though clearly the
metric of 20 on our external

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would have been a lower
cost, we see that that's not

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what made the decision here.

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The decision came down to
internal beats external.

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In this video, we just
did a quick demonstration

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that regardless
of lowest cost, it

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doesn't matter if one route is
internal and one is external.

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That internal route
will always win.

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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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