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When configuring OSPF. NBMA topology one needs to define neighbor AND DR/BDR manually.
If I pick the option point-to-multipoint non-broadcast
and I do:
'ip ospf network point-to-multipoint non-broadcast'
There is no DR/BDR election and I do need to define neighbors manually.
That said, my question is:
In which occasion one would use
point-to-multipoint non-broadcast ? Is that practical ?
Isn't a 'point-to-multipoint non-broadcast' the same thing than NBMA ?
I am not sure if I see the difference here.
Try to check below link for the OSPF design guide.
The NBMA is the type of network. The pt-to-multipt is the type of interface.
If you config. the OSPF w/ "non-broadcast", it will not broadcast the hello, so you have to manual config. the neighbor.
Therefore, in NBMA, you can config. the network type as "broadcast" then the neighbor will be up due to broadcast the hello actively.
Another link for your reference.
Hope this helps.
And the explanation below makes me understand why the concept of DR/BDR on point-to-multipoint is not applicable:
"...An OSPF point-to-multipoint interface is defined as a numbered point-to-point interface having one or more neighbors. This concept takes the previously discussed point-to-point concept one step further. Administrators do not have to worry about having multiple subnets for each point-to-point link. The cloud is configured as one subnet. This should work well for people who are migrating into the point-to-point concept with no change in IP addressing on the cloud. Also, they would not have to worry about DRs and neighbor statements. OSPF point-to-multipoint works by exchanging additional link-state updates that contain a number of information elements that describe connectivity to the neighboring routers.
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