OSPF - DR/BDR Elections process, broadcast/non-broadcast

lon21lon21 Member Posts: 201
Hi,

I'm just learning on OSPF.

I know that 'No DR is assigned on any type of point-to-point link. Also no DR/BDR is assigned on the NBMA point-to-multipoint due to the hub/spoke topology. DR and BDR are elected on broadcast and non-broadcast multi-access networks. Frame Relay is a non-broadcast multi-access (NBMA) network by default'

But I'm having extremely difficulty in remembering this, it would really help with my memory to understand why these selections are only specific to certain broadcast/non-broadcasts?

Thanks

Comments

  • nethackernethacker Senior Member Member Posts: 184 ■■■□□□□□□□
    lon21 wrote: »
    Hi,

    I'm just learning on OSPF.

    I know that 'No DR is assigned on any type of point-to-point link. Also no DR/BDR is assigned on the NBMA point-to-multipoint due to the hub/spoke topology. DR and BDR are elected on broadcast and non-broadcast multi-access networks. Frame Relay is a non-broadcast multi-access (NBMA) network by default'

    But I'm having extremely difficulty in remembering this, it would really help with my memory to understand why these selections are only specific to certain broadcast/non-broadcasts?

    Thanks
    constant reading will help u out... the more you read it,the more it sticks.
    JNCIE | CCIE | GCED
  • ZartanasaurusZartanasaurus Member Posts: 2,008 ■■■■■■■■■□
    lon21 wrote: »
    Hi,

    I know that 'No DR is assigned on any type of point-to-point link.
    If you can remember this, you can remember everything else.

    Point-to-multipoint is a collection of point-to-point links. And point-to-point links don't elect a DR/BDR. Therefore, point-to-"X" interfaces = no DR/BDR. Everything else = DR/BDR election.

    Broadcast/non-broadcast determines how neighbors are formed. In a broadcast network, neighbors are formed automagically. In a non-broadcast network, you have to configure neighbors statically with the neighbor command.

    If you can remember those two groups (point-to-"X" v everything else and broadcast v non-broadcast), you should be able to identify what the network should look like.

    If I say "point-to-multipoint non-broadcast" you just go down the list and perform the logic.

    Point-to-mpoint = no DR/BDR election
    non-broadcast = neighbors configured statically

    Interface type determines whether or not a DR/BDR is elected.
    Broadcast type determines how neighbors are formed.
    All DRs/BDRs are neighbors, but not all neighbors are DRs/BDRs. ;)
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  • nethackernethacker Senior Member Member Posts: 184 ■■■□□□□□□□
    If you can remember this, you can remember everything else.

    Point-to-multipoint is a collection of point-to-point links. And point-to-point links don't elect a DR/BDR. Therefore, point-to-"X" interfaces = no DR/BDR. Everything else = DR/BDR election.

    Broadcast/non-broadcast determines how neighbors are formed. In a broadcast network, neighbors are formed automagically. In a non-broadcast network, you have to configure neighbors statically with the neighbor command.

    If you can remember those two groups (point-to-"X" v everything else and broadcast v non-broadcast), you should be able to identify what the network should look like.

    If I say "point-to-multipoint non-broadcast" you just go down the list and perform the logic.

    Point-to-mpoint = no DR/BDR election
    non-broadcast = neighbors configured statically

    Interface type determines whether or not a DR/BDR is elected.
    Broadcast type determines how neighbors are formed.
    All DRs/BDRs are neighbors, but not all neighbors are DRs/BDRs. ;)

    i can't help but say thank you..this is very helpful
    JNCIE | CCIE | GCED
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