And then lost me the stub area flag needs to be the same the step area flag denotes whether this is
a stub area or a normal area.
We'll talk more about stub areas once again in later slides.
Now let's talk about designated roads and backup designated route as in this typologies have six routers
connected to the same Ethan that segment so soon the D6 route is connected to a switch or a hub all
sharing the same ethernet segment designated routers or Dior's are used on broadcast multi-axis environments
such as Ethernet and so when implementations such as non-broadcast multi-axis environments in Frame
Relay So do explain why we have a designated Harada let's assume that this network 10 1 1 0 is connected
to of one and the routers are connected to this.
Ethan its segment and assume that this network goes down.
So let's assume for the moment that there's no designated router on this Ethan that segment.
And hopefully you'll quickly see why there is a requirement for designate Harada with to designate RATO.
All of these routers would have a full adjacency in a full adjacency elysées are exchanged between routers.
So in this example all one needs to notify the other routers using a links they update that there's
been a change in the network topology or one will send an update or three send an update to our team
2 or 4 2 or 5 or 6 notifying all of the rods that there's been a change in the typology or two when
receiving that update from or one.
In this case because there is no designated Rodda has a full relationship with all other routers.
So it sends an update to all of its neighbors to notify them that there's a problem.
The same will happen on our three or three receive an update from our one so it notifies all of its
neighbors that there's been a change in that apology or we'll do the same thing it received an update
from or one.
So it sends an update to all of its neighbors and I'm sure you're getting the picture now or five received
that update from our one.
So it sends an update to all of its neighbors and lawlessly or six sends an update to all of its neighbors.
So there's a lot of duplicate traffic when a single network goes down and these six routers have a full
adjacency with one another.
So rather than doing that a designated route is selected on the specific segment.
So let's assume that or two was elected as a designated Rodda designated route is selected on two criteria.
The first one is highest priority.
You can specify the priority on an interface the default priority is 1 0 excludes Arado from becoming
a designated Rodda or backup designate Harada the values for the priority are from 1 to 255.
So the first criteria is high priority if the priorities are the same then the Rotto with the highest
Rodda ID is elected as the designated route for that segment.
So in this example we've elected or to use the designated route.
And let's assume again that this network goes down.
But what happens now is or one sends an update only to the designated rodders designate or out as a
listening on this multicast address 2 2 4 0 0 6 other voters are not listening to that multicast address.
So from an IP point of view they do not receive or see that update only the designated Harada receives
that multicast update.
Now multicasting isn't covered in this course.
But briefly this infrastructure was a hub so the roads were connected via a hub at least one that multicast
would go to all the routers.
However only certain routers are listening or accepting that multicast.
So only certain routers have subscribed to that multicast.
In this case only designate Iran are listening for and accepting multi-process to address 2 2 4 0 0
6.
So the other odd is at least two will drop this update.
OSPF residing at least for now is our model will not see this update.
On the other rodders serratus 3 4 5 and 6 from an OSPF point of view low will not receive the update
on the router to will receive the update so logically what happens.
The link goes down Route 1 is updating Rodek to the designated router by sending a multicast to the
address on the router to the designated routers receiving the multicast router to then sends an update
to all the other riders on this multicast address to do for the 0 0 5.
All OSPF routers are listening to this multicast address so they will receive the update Router one
would receive the update.
They wouldn't process it because it's always typologies tables are already up to date.
So logically what happens is the update goes from one or two parties sends an update to all the other
routers.
They process the update and they feel that apology database is updated with the new information that
this network has gone down.
As you can see here it's much more efficient to use a designated router than to allow full adjacencies
between all routers and have all those duplicate updates.
It's important to realize that only the designator outer and backup designator Rotto will have full
relationships to all the other bodies.
So for instance route 4 and 5 will only have a state known as Two way in two way.
They know about each other but no updates will be exchanged between the routers.
So in other words are 4 or 5 will not update each other.
Neither will are five or six and so forth and so on all rodders will only update the designator outer
and backup designated router with changes in the topology so they have a full relationship to the designated
router.
This allows for the saving of updates and duplicate traffic on a single segment.
Once again it's important to realize that Rochus on the segment will only form full relationships with
designator routers and backup designator outhe's.
Now in this example I've only got a designated router.
The issue with only having a designated router is that if this router goes down updates will not be
sent and received properly.
So on a segment a designated router will be elected and normally a backup designator auto would also
be elected.
So you'd have both a designated router and backup designator outta the BBR will become the Diyar if
the deal fails.