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Difference between Broadcast network and NBMA in OSPF.

mirzaakberali
Level 1
Level 1

why does DR/BDR is not required in pint-point ospf network.Can some also let me know how to calculate cost in ospf.

18 Replies 18

then where we use broadcast and non broadcast (NBMA) in ospf...in both DR/BDR is selected..please help...

To the point answer! thanks....

Some additional notes on OSPF costing.

If I remember correctly, OSPF, strictly speaking, doesn't require bandwidth to map into the cost metric. However, as Mohammed notes, Cisco (starting with IOS 10.3) assigns a cost of 1 to links with 100 Mbps. Not all vendors do this, or use the same base bandwidth. If you mix vendor equipment, you might want to insure all costing is playing by the same rules.

Second, if you use 100 Mbps Etherchannel, gig or 10 gig links, by default, they too get a cost of 1. This means OSPF can not see the difference between links 100 Mbps or better. This can be dealt with by moving the base bandwidth metric to represent the highest speed, using the command "auto-cost reference-bandwidth mbps", or by setting the cost on every interface manually.

Lastly, if you have network that's deep enough with low bandwidth links while running on a higher base reference bandwidth, the cost counter fills. Once again, OSPF will be unable to determine which path is better.

What is the difference between broadcast multi access point and non broad cast multi access point ?

 

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