In this video we're going to discuss OSPF Designated Routers Orders and Backup Designated Routers or
PDR.
This is one of multiple videos.
And in this first video, let's see if we can answer some basic questions in this topology.
How many designated routers are there?
In other words, how many doors will be elected in this topology?
Second question how many backup designated routers or bidders are there in this topology?
And thirdly, how many Dior, others or druthers are there in this topology?
So can you answer how many doors, how many borders, how many are others are there in this topology?
Notice that rather one, rather two, rather three and rather four are connected to a layer two switch.
There's no configuration on the switch.
Rather four is connected to right of five via serial link and router five is connected to right a six
via an ethernet link.
How many doors?
How many bidders?
How many others?
So let's configure the topology and find out.
In this topology I've only configured IP addresses.
I haven't configured OSPF.
Some rather one show IP protocols.
OSPF is not configured.
Let's paste a basic OSPF configuration onto the router.
We've enabled OSPF on all interfaces on the router show IP OSPF interface brief.
OSPF is enabled on gigabit zero zero.
Current state is wait.
That's this link here.
Gigabit zero zero is the link to the switch.
After a while the state should change, but the rot awaits to see if other routers are configured on
the same segment.
In this example, the Rada has become the designated Rada.
That would make sense because there are no other routers configured on the Layer two switch.
I brought it to.
Show IP protocols.
OSPF is not currently running.
Paste the OSPF config in.
Neighbor relationship has been established and the state has gone to full.
Show IP OSPF neighbor.
We can see that Ratu has formed a relationship with rather one.
Rather one is the D.R..
A full relationship exists to that.
Rather.
Show IP OSPF interface brief shows us that the local router is a backup designated router.
What about rather three show IP protocols?
OSPF is not currently enabled on this router, so I'll paste in the configuration.
The Rada has formed two neighbour relationships one with Rada one one with writer two so show ip ospf.
Interface brief OSPF is enabled on the local gigabit zero zero interface.
The router is a driver.
In other words.
OSPF is running on this interface.
Gigabits.
Zero zero.
Router three has become a D.R. other.
Or rather.
So ip ospf neighbor to neighbor relationships exist one to write a one who's the D.R. another to write
a T which is the border notice full relationship, which means that rats are exchanged between these
routers.
So rather three will synchronize its OSPF database with router one and router two.
Okay.
So router four.
Show IP protocols.
OSPF is not enabled on this router.
The output is different here because this route is running version 12.4 of iOS, whereas these other
routers are running 15.6.
They are iOS v routers, whereas this rather is a C 3725 router.
So IP protocol shows no routing protocols.
I'll enable OSPF on all interfaces on this router.
Show IP ospf interface brief.
The Shroud is acting as a driver on the fast Ethernet interface and it has a point to point connection
on the serial interface.
We can see that a relationship was formed to router two and rather one.
So show ip ospf neighbor.
It only forms a full relationship with rather one and rather two.
In other words, the D.R. and the BTR.
It does not form a full relationship with RADHA three.
On Rota three, we should see something similar.
Previously, Rada three had a full relationship with Rather one and rather two.
It still has that, but it has a two way relationship or half formed relationship with Ratu for.
So in this Ethernet segment, we have one ADR will ADR and BD will be elected on this link.
So let's test that.
Here's rather five.
So IP protocols, no protocols are running.
Let's enable.
OSPF.
Show IP OSPF interface brief OSPF is enabled on the serial interface as well as the Fost Ethernet interface
of Router five.
So it's running here and here.
Currently it's set to weight on fast Ethernet it's point to point on the serial.
Notice Stol point to point on the serial.
Show ip ospf neighbor.
The strata has a full relationship to write a for.
But we don't have an election.
OSPF, D.R. and BD elections do not take place on serial point to point lengths.
So in front of Fool once again, it's formed a full relationship to write a five.
But no election took place on the serial link.
On the serial interface, there was no election.
An election did take place on the Ethernet link.
And therefore we have a D.R. PDR, and in this example, another D.R. or other.
So on this part of the network, the switch, we have a designated rider elected.
No designated rider was elected on the cereal link.
What about on this Ethernet link between route of five and router six?
So back on Route five, notice four out of five became the designated rudder on this segment because
there are no other rudders running OSPF on that segment.
So if we enable OSPF on router six, what happens?
Show IP OSPF interface brief router six has become a BTR.
It's formed a relationship with router five show IP OSPF.
Maybe.
We can see that rata five is the designated rata full relationship between Rata six and Rata five.
Rata six is the BTR.
So in answer to the questions, how many dollars are elected in this topology?
Answer is two.
How many bidders are elected in this topology?
The answer is two.
Rather one, and out of five are designated routers.
Router two and router six are backup designated routers or bidders.
Rather three and rather four on the segment.
Are Dior others.
So what you need to know is that a designated rider is elected on a per segment basis, but only on
broadcast multi axis or non broadcast multi axis links.
In other words, links or interfaces where you can have more than one router connected to that single
segment or single subnet.
So as an example, if we added another link between Rider one and.
Without a fall we would end up seeing.
That one of these routers is the designated router on this segment.
And to show you that errata can be a D.R. as well as a BD, R or D or other.
What I'll do.
Is no shut the link en route of for first.
And configure router for first so that it becomes the D.R on that link.
So show IP OSPF interface brief.
On Fost Ethernet zero one.
We are in the Wheat State.
So it's waiting for another router.
Might take it a while.
So while we're doing that, let's configure.
An IP address on router one, but I won't know.
Shut the interface so that interface is shut.
I'll configure an IP address on the interface, but I won't know.
Shut it yet.
Notice what a fool has become the designated rider.
On this segment.
So now in rata one aisle.
No, shut the interface show IP OSPF.
Interface brief relationship is formed.
And when I press enter now we can see that rata one is a backup designated router on gigabit zero one.
So we've changed the topology slightly.
Now we have a designated rider, which is rider one over here.
A designated rider here, which is rather full.
And it designated rider here, which is rather five.
Rider six is a backup designated rider on this segment.
Under this layer two segment, router two is a backup designated rider.
And on this segment, rider one is a backup designate.
A rider.
So notice on Rider one.
It's a designated Rada on one segment and a backup designated rider on another segment.
Designated Riders backup.
Designated riders are chosen on a per segment basis, but only on multi access networks or segments.
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I wish you all the very best.