[AUDIO LOGO]
So in the last video, we saw the showdown between internal
versus internal routes.
But what about external versus external?
Now, externals don't have that same marking, so to speak,
of being either from your own area or from a different area.
However, there are two different types of external routes.
There's external type 1 and external type 2.
Now, generically speaking, what that means is with a type 2,
we're going to not track internal cost.
Now, we'll see in our upcoming videos that in a way,
we still sort of do because there's something
called the forwarding metric.
And we have to look at that.
However, it's not stored right in the metric of the route.
With a type 1 external, the metric for the route
is actually calculated by looking not only at the type 5
LSA but also by looking at the distance or the cost
to the exit.
That is then put together into the metric
in the routing table.
And we'll see this as we go.
But as always, let's start by jumping into our topology,
taking a look at what we're going to build,
and then jumping into the command line
and seeing all of this work.
As we jump into this demonstration,
it is important to note that the previous internal instances
of this route that were on router 8 and router 5
have at this point been removed.
We now just have the one instance on router 10.
Again, this is of the 100.100.100.0/24 network.
This is being redistributed on router 10 into OSPF.
And it's coming in as the default
type of an external type 2.
We're going to start by examining that external route.
As per usual, we'll take a look at it on router 7.
And then what we're going to do is
we're going to create this loopback on router 5 again.
But this time, we're not going to bring it in as internal.
We're going to redistribute this into OSPF
and bring it in as an external type 1.
So we're going to create this type 1 external.
And we're going to give it a high cost.
Again, we're trying to prove the rule
that the E1 will be believed over
the E2 regardless of the cost.
That's the point of this.
So by bringing it in with a high cost,
we'll be able to prove that.
We'll also examine a little bit about that E1, how
the metric looks, and so on.
So we will not only be observing that the type 1 beats the type
2, but we'll also see what the E1 looks
like as far as the metric in both
the LSA and the routing table.
So let's jump in and get started by looking
at that route on router 7.
So if we look at the routing table here on router 7,
right now, it's an external type 2.
And it has a metric of 20 and a forward metric of 2.
Keep these numbers in mind as we go through this demonstration.
Now, one other thing to note, if we look at the database itself,
notice the metric here is also listed as 20.
So one of the fundamental characteristics
of the external type 2 is that the metric shown
in the routing table, in this case 20,
is the same as the metric shown in the database on the type
5 LSA--
again, in this case a 20.
Now let's bring in a type 1.
So let's go over and do this on router 5.
So on router 5, we'll make our new interface loopback 100
interface.
But this time, instead of actually running OSPF on it,
we're instead going to go into router OSPF 1.
We'll do a redistribute of connected routes.
We'll set the metric type.
And of course, we have our two choices here.
The default is metric type 2 if you don't specify.
We're going to specify a metric type of 1.
And as we mentioned previously, we're
going to set this to a rather high metric.
Let's just set it to 5000.
We can verify this if we do a show ip ospf database external.
And we'll filter it by self originated.
And we see exactly what's going on here.
We see that it is a metric type 1.
And we see that it has that metric of 5000.
So now let's, of course, go back to router 7
and observe what's happening.
First thing we're going to do on router 7
is look at the database again.
So let's again look at that same exact command.
But of course, this time we have this new LSA,
the one from advertising router 10.5.5.5.
Notice the metric.
The metric is still 5000.
Here's the thing with the type 1 external.
It does track internal cost when it puts the route
into the routing table.
But here in the database, notice that it still
has this metric of 5000 through the entire network.
The type 5 LSA itself is never changed.
But what the type 1 external tells the receiving router
to do is to take this metric of 5000 and add it to our cost
to the exit.
Let's take a look at how that's put together.
So if we were to say show ip ospf border,
notice that our cost to get to our advertising router
of 10.5.5.5, it actually has a cost of 3,
which means that if I say show ip route for the 100.100.100.0,
that means that the metric shown in the routing table is
actually 5003.
That's the 5000 coming from the type 5 LSA added to the 3
that it costs me to get to the advertising router.
Now, since I have two equal costs to get to the advertising
router, you can see here we are, in fact, doing load sharing
as well to this new route.
So two big things we saw in this video--
number one is that that external type
1 beats the external type 2, regardless of the metric.
Once again, we started off with a route with a metric of 20.
Now we have a route with a metric of 5003
just because it's a type 1.
The other thing is when you have that external type 1,
the actual type 5 LSA itself is not
modified, except for the fact that it says
that it's a type 1, of course.
But what that type 1 indicates to the receiving device
is that it should take the metric from the type 5 LSA
and add that to the cost to get to the advertising router
when it puts that route into the routing table itself.
That way, the routing table reflects the total costs
to get to that route.
I hope this has been informative for you,
and I'd like to thank you for viewing.