Difference between NBMA vs point-to-multipoint NB (OSPF)

Answered Question
Oct 2nd, 2006

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.

I have this problem too.
0 votes
Correct Answer by jackyoung about 7 years 6 months ago

Try to check below link for the OSPF design guide.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

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.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009470d.shtml

http://www.cisco.com/en/US/products/sw/iosswrel/ps1826/products_feature_guide09186a0080087d4e.html

Hope this helps.

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Correct Answer
jackyoung Tue, 10/03/2006 - 00:23

Try to check below link for the OSPF design guide.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

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.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009470d.shtml

http://www.cisco.com/en/US/products/sw/iosswrel/ps1826/products_feature_guide09186a0080087d4e.html

Hope this helps.

news2010a Tue, 10/03/2006 - 06:28

Perfect.

And the explanation below makes me understand why the concept of DR/BDR on point-to-multipoint is not applicable:

Point-to-Multipoint Interfaces

"...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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Posted October 2, 2006 at 8:35 PM
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