How does ospf elect dr

One thing i think people should take in mind is that according to cisco, the DR is elected first:. Hello packets are exchanged via IP multicast packets Appendix B on each segment. The same process is repeated for the BDR.

In case of a tie, the router with the highest RID will win. The default for the interface OSPF priority is one. The following diagram illustrates the DR election:". In page of the CCNP ocg does not say much:. These functions include the generation of LSAs. I think you're reading too much into that Cisco document. I'm not sure why people are confused - Esummers pointed out the reason for the BDR being elected first - to bring order to the process.

Since the current DR is not challenged by the old DR after it comes back up it means that the most stable router will be the DR. In practice it means the highest priority router will be DR from startup but after that it may not always be the case. There is nothing to be confused about.

If unsure please refer to cisco documentation if you are going for a cisco exam , if your just curiouse about how link state algorithm works then take your time, its nice reading, but kss. I do know how LS algorthms work. I assumed from your post that you were confused because you actually stated that it was confusing so I was trying to clarify things for you. Apologies if it confused you further. Hopefully no harm done. If you encounter a technical issue on the site, please open a support case.

Communities: Chinese Japanese Korean. All Rights Reserved. The Cisco Learning Network. Enterprise Certifications Community. View This Post. Edited by Admin February 16, at AM. Top Rated Answers. The RFC explains why: "The reason behind the election algorithm's complexity is the desire for an orderly transition from Backup Designated Router to Designated Router, when the current Designated Router fails.

Hope this helps! Good luck. All Answers. Hi nuno Thank you very much for writting but my question here is why first bdr is elected, i mean in the intal stages when the ospf being configured in a fresh network its given that bdr is elected followed by dr this my confusion, i dont get it at all. I am clear on the part which you have explained. Hi, Esummers is right. But i created as a serial interfaces without using the NBMA there is no election process. Why it can't forms.

I posted a topic in the same question. Thank you Great article. I never thought about what would happen if you withdrew the DR from the OSPF topology with all the routers set to not participate in the election process. You can approximate NBMA networks with point-to-point serial interfaces by using a frame relay switch in the middle and having the broadcast command configured in your frame-relay map. Perhaps you have confused NBMA with point-to-point serial interfaces due to the interface type used?

If you connect routers to other routers using a serial link then they're point-to-point networks, not NBMA networks. Would changing the OSPF priority at one of the interface end points of the tunnel result in the adjacency being formed?

All, I got it working. It was due to a rogue static route pointing to one of the tunnel interfaces. I made the same mistake as a newbie. I believe what had happened here is that you have two separate segments i.

Since this is the case your router is DR for both of these broadcast domains. What are the timer involved in the background,if any? Can you please explain? This concise and clear look at OSPF neighbors helped me keep this sorted out for a recent certification exam, thanks! Wonderful article at the same time it is written amazingly simple words that made it very easy to understand at 1st sight.

Hi Jeremy, what will happen if we configure the highest priority router at the end? Is there any way to make the Router is DR even though the priority for this router and the router ID isn't the highest?

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Thanks, Paul. Bored AT Work June 3, at p. OmiPR June 3, at p. Great article Stretch! Curious Yellow June 25, at p. Kaustubh October 11, at p. I am not able form OSPFv3 adjacency between the 2 end points of the tunnel.

Any suggestions? Cheers, Kaustubh.