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I read somewhere that the forwarding of data traffic is interrupted when the DR of an OSPF network fails. Why is this so? As per my understanding, the network LSA originated by the DR is still present in the AS, and that would describe the routers attached to the network, and should still allow the data traffic to be forwarded to that network. Then why is it that failure of DR should interrupt data traffic? Can any OSPF experts help with this doubt?

Anand S Kumar
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user1510194
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  • Hi, can any ospf experts please help here? I thought this should be a simple question for people who have worked on ospf for some time... – user1510194 Mar 18 '13 at 18:01

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OSPF detects changes in the topology, such as link failures, very quickly and converges on a new loop-free routing structure within seconds. ospf

If you lose a DR on a broadcast network, there is no communication between the rest of the routers until a new DR is elected, this can take afew minutes, if you dont have any BDR. By having a BDR already in place, this cuts down the protocols "lack of visability time".

By having only 1 DR, a link may fail and this failure will not be discovered by ospf for a few minutes until a new DR is elected, traffic could be unnecessarily block holed for a couple of minutes even if there is a backup route present in ospf.

It depends on what your configuration is, i.e. Do you have only 1 DR(& no BDR) topology. Otherwise as specified in OSPF Documentations, it recovers quickly from link failures.

Not an OSPF expert, but(can deduct) OSPF also has limitations, and in certain topologies, it can also fail(i.e. data traffic can be interrupted), but which is not the general case.

Community
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a.m.
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  • Thanks for the response. The case of a link failing when DR is down makes sense in understanding how DR being down (and no BDR being present) could cause a problem in data traffic. – user1510194 Mar 19 '13 at 15:35
  • But the RFC also says that even if BDR is present, there will be a period of disruption in transit traffic till the LSAs announcing the new DR are flooded. My doubt is: why should there be disruption in "data" traffic in this case? Routing traffic may be interrupted but what does DR/BDR have to do with forwarding of data traffic via transit networks (Assume there is no link down case like in your example)?I thought DR/BDR concept was only for optimizing the amount of routing protocol traffic; I do not understand their significance in forwarding of data traffic. – user1510194 Mar 19 '13 at 15:42