CCNP ROUTE: 7.Influence DR/BRD election without changing RIDs, using a single command (make R1 - BDR, R2 - DR, R3 - permanent DROther)

R3(config)#int fastEthernet 0/0
R3(config-if)#ip ospf priority 0   (this command sets Fa0/0 priority to 0, from the default of 1, making R3 permanently DROther)

Now, having equal priorities, R1 and R2 remain in the DR/BDR process and R2 (the former BDR) takes the role of DR and now R1 is chosen as BDR.
R3#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/BDR        00:00:36    192.168.0.1     FastEthernet0/0
2.2.2.2           1   FULL/DR         00:00:37    192.168.0.2     FastEthernet0/0

Even if we set R3's priority back to 1, R3 will not become DR again, until reloading all 3 routers.
Even if we set R3 with the highest priority of all 3 routers (value of 2), R3 will not become DR again, until reloading all 3 routers.
R3(config)#interface fastEthernet 0/0
R3(config-if)#ip ospf priority 2

R2#show ip ospf neighbor                                                

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/BDR        00:00:33    192.168.0.1     FastEthernet0/0
3.3.3.3           2   FULL/DROTHER    00:00:38    192.168.0.3     FastEthernet0/0

Now, R2 is the DR. If we reload the current R2, then R1 (the current BDR) will be elected as DR, R3 (although it has a greater priority than R1) will be elected as BDR and R2 will return as DROther.
R1#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
9.9.9.9           0   FULL/  -        00:00:38    192.168.0.22    Serial0/0
5.5.5.5           0   FULL/  -        00:00:38    192.168.0.18    Serial0/2
4.4.4.4           0   FULL/  -        00:00:38    192.168.0.14    Serial0/1
2.2.2.2           1   FULL/DROTHER    00:00:38    192.168.0.2     FastEthernet0/0
3.3.3.3           2   FULL/BDR        00:00:38    192.168.0.3     FastEthernet0/0

Also, if instead initially setting R3's priority to 0, we would have reloaded the router, R2 (the former BDR) would've taken the role of DR and R1 of BDR, with a reloaded R3 as DROther.

After reloading all 3 routers, regardless of the current DR/BDR roles (and with the default priorities), the initial roles are put in back in place:
R1#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
9.9.9.9           0   FULL/  -        00:00:37    192.168.0.22    Serial0/0
5.5.5.5           0   FULL/  -        00:00:30    192.168.0.18    Serial0/2
4.4.4.4           0   FULL/  -        00:00:30    192.168.0.14    Serial0/1
2.2.2.2           1   FULL/BDR        00:00:38    192.168.0.2     FastEthernet0/0
3.3.3.3           1   FULL/DR         00:00:39    192.168.0.3     FastEthernet0/0

The rule is: After a DR and BDR are elected, no election is held until either the DR or BDR fails. If the DR fails, the BDR becomes the DR–—regardless of
whether a higher priority router has joined the subnet—and a new election is held to choose a new BDR. If the BDR fails, a new election is held for BDR,
and the DR remains unchanged. Also, note that for serial interfaces (point-to-point) the default OSPF priority is 0 and it cannot be modified:

R1(config)#interface serial 0/0   (link to R9)
R1(config-if)#ip ospf priority 3
R9#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           0   FULL/  -        00:00:39    192.168.0.21    Serial0/0