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jskfanFlag for Cyprus

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OSPF DR and BDR

I would like to know in which topology DR/BDR will be formed.
I know that it automatically forms in a Broadcast segment, but I wonder if it means full mesh ?

example:
R1 is connected to R2 and R2 is connect to R3 and R3 is connected back to R1, This is Broadcast segment and the DR/BDR election will occur..

What if :
R1 is connected to R2 and R2 is connect to R3 but  R3 is not connected  to R1. I believe this is not Broadcast and not full mesh, as such no DR/BDR election...

What if:
R1 is connected to R2 and R2 is connect to R3 and R3 is connected back to R1,and there is another R4 connected only to R1... would R4 participate in DR/BDR elections ?

Thanks
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<<<Also, keep in mind that DR/BDR election also only occur per segment>>>
the only way I see you can connect 3 or more routers into the same segment is if you use a Switch.

if you  connect only R1 to R2, that will be point to point ,regardless if it is serial or Ethernet interface. so there will be no DR/BDR . correct ?

if you connect R1 to R2 and R2 to R3,  they got to be in different segments, and there will be no DR/BDR. correct ?

I also want to confirm that DR/BDR not only requires routers to be in the same network segment, but also in the same OSPF area . Correct ?

Thanks
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<<<if you connect R1 to R2 and R2 to R3,  they got to be in different segments, and there will be no DR/BDR.>>>

I need to try it....because in this case R2 will have 2 different interfaces in the same subnet... I do not think it will let you do that...
Can R2 have one interface with 192.168.1.10 and another interface with 192.168.1.20 ??
Is there a diagram somewhere that I missed?
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Ok...
I did not know that DR/BDR depends also on medium (Ethernet vs serial)
To me point to point means there is no switch or else between the routers...
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Thank you Guys!