This is one of multiple videos discussing the wispy FDR and video designated Rada and become the designated
Rada.
Elections and selection criteria on Cisco we have this document that says that dealers and BDO elections
are done via the hello protocol Hello packets are exchanged via multicast packets on each segment.
The Rada with the highest priority on the segment will become the D.R. for that segment.
The process is repeated for the PDR in the case of a tie.
The Rada with the highest Rada idea will win the default property on an interface is one if you set
the primary to a zero.
It means the Rada will not become a ADR or a PDR.
Remember that the D.R. and BDO concepts are per multi access segment.
Setting the OSP of priority on an interface can be done using the IPO SPF Prodi command.
Now let's look at the segment that has rather 3 rather 2 to 1 and read a full connected to it on the
segment rudder one has neighbor relationships to rudder to rudder three and wrote a full note to the
interface gigabit zero the stop entry is for the segment on gigabit 0 1 but we are concentrating on
gigabit to 0 0 for the moment so we don't see a D.R. show IP or SPF interface brief what we do see is
that the local Rata a one is the designated Rata.
Now that goes against what we've just read the runner idea of this strata is lower than the other Rod
is on the segment and this is where real world comes into play versus theory.
The reason why Russia won was elected as the designated Rada is that in the previous video I configured
Rada 1 first before I configured the other.
So Rada 1 was the only Rada on the segment it was waiting for other.
None appeared so it became the D.R. when the other rods were added to the segment and I added them in
the order of Robert to then Rada a three then Rada for RADA one was already the designated Rada once
a designated Rod is elected and a Roddick comes on to the segment with a higher priority will higher
Rod I.D. It's not going to usurp or pre-empt the designated Rada the designated Rada remains the designated
Rada and hence the local Rada with a lower rate I.D. which we can see by using the command show IP was
interface
is elected as the D.R. on gigabit 00 because it came on line first notice it has an adjacency or neighbor
relationship with three routers brought it to is the backup designator Rada wrote a three and root a
four R D or others show IP SPF and neighbor Rod it to is a PDR a 3 wrote a 4 or D or others on gigabit
00 so what happens if we go on to gigabit 00 and we top IPO SPF priority 0
show IP SPF interface what you'll notice is the a state on gigabit 00 has changed to D or other it's
now formed a full relationship to rather to show IP SPF neighbor rather one has a full relationship
to brought broader two as well as Rod four.
The reason why Rod it too became the D.R. is it was already the BTR and then out of Rod it 3 and Rod
of 4 Rod of 4 became to the BTR because it had a higher Rod I.D. So the theory is as follows.
Rod it with the highest property becomes designated rata on a segment that's not entirely true.
If one Rodda comes into the segment first before other Rod is that Radha will be the designated Rod.
But if that all come online at the same time it's based on highest priority then highest Rod I.D. then
highest loop back interface ip address then highest configured physical interface address.
And in this case Rod a fool became the backup designated rider because it had the highest IP address.
So what are going to do now is reboot the switch so that you can see the full process of how the exam
explains how ideas are elected so first thing I'll do is change the protein of rod to 1 back to 1 on
Rod a 2 to let's confirm the relationships show IP SPF neighbor Rod a 1 is a D or other Rod a 3 is a
D or other Rod a 4 is a backup designated Rata and the local Rata is a designated Rata in the output
show we can see there are of 4 is the backup designated Rada wrote a 3 and Rod a 1 or D or others.
So let's see what happens when we shut down interfaces on the switch so shut down a range of interfaces
gigabit 0 2 3 so shut those interfaces down.
On router 1 show IP 0 SPF neighbor not may take it a while ingenious 3 to realize that the interfaces
have gone down.
So what I'm gonna do at this point is pause the video and what we should see is that these states change
so after a while the dead timer expires for the neighbor relationships.
Previously we had these neighbor relationships and now those neighbor relationships have disappeared.
The only neighbor relationship that to one has is to rot for using this Ethernet link
so to ensure that it doesn't get confusing I'll shut that link down as well.
So we have no always P.F. neighbor relationships on route one at all.
The switch has all of its interfaces shut down once again.
So let's have a look.
On rudder to show IPO SPF neighbor no neighbor relationships and write it to write a three show IPO
SPF neighbor no neighbor relationships a for show IPO SPF neighbor.
It only has a neighbor relationship on the surreal interface not on the Ethernet interface Serato for
has a neighbor relationship to rot a five but no other neighbor relationships so on the switch no shut
we've enabled all the interfaces on the switch so in a one off to a period of time we should see that
neighbor relationships are formed.
We can do a ping to check if the interfaces have come up
interfaces are starting to come up on the switch pings are now succeeding.
And now we see maybe relationships three neighbor relationships have been formed on a once a show IP
SPF neighbor brought one has a two way relationship to rot it to rot a fool has become the designated
Rada and a three has become the backup designated Rada.
The reason why Rada 4 became the designated Rada is because it has the highest IP address on any physical
interface this interface has an IP address of 10 1 1 1
this interface on brought it to its 10 1 1 2
this interface on Route 3 is 10 1 1 3 this interface and a force 10 on 1 1 4.
But in addition it has an IP address on the serial interface of 10 1 2 1.
So because it has the highest IP address of any physical interface
it becomes the D.R. with this IP address.
The reason why it didn't use this IP address is because this interface was added after the 0 SPF process
had run.
So the Rada I.D. had already been selected these two interfaces were up when OSP started this interface
wasn't up when 0 SPF was started.
So the Rada idea that was chosen was 10 1 to 1.
So that proves that the Rada with the highest IP address of any physical interface will become the designated
Rada on a segment when all the devices come up.
Let's see if we can change that by manipulating priorities.
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