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I know the DR/BDR and ABR are of course separate concepts and serve different functions, but in many cases is the ABR router for a given area also made to be the DR? Or would the DR be more often an internal router in an area? I'm guessing it doesn't necessarily matter, or that the latter is more true, but I haven't seen actual production network examples. I get that the DR is the sort of "leader" or main representative for the area its in, so that the other routers in the area are connected primarily to it and don't need to know the routes to every other router in the area, thus saving some overhead and processing. The Area Border Routers merely serve to summarize the routes from the other areas and advertise them into the others they're connected to... meaning to the DR of that area? Like is that what a Type 3 LSA is essentially?

Also, as a related question... what exactly is this "non-broadcast multi-access" network connection type that keeps getting mentioned in these contexts? It's not explained well in the books I've read for the cert.

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin ♦
    Dec 25, 2018 at 9:45

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Hi and welcome to Network Engineering! I think you are misunderstanding the concept of a Designated Router. The DR applies only to a single network segment, not the entire area. DRs are used for broadcast-type network segments (most commonly, Ethernet). There may be many Ethernet segments in an area, so there will be many DRs.

That has nothing to do with the area concept, which is used to control flooding and limit route calculation.

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  • Ah right. I can't believe I forgot that. I took a hiatus from networking topics for a while and am trying to dive back into it. So this DR/BDR situation would apply when say there are several routers connected by a common switch in between them? A broadcast multi-access network. As opposed to point to point WAN links, where there is no election process.
    – Addy Lupe
    Oct 12, 2018 at 14:57
  • That is correct.
    – Ron Trunk
    Oct 12, 2018 at 15:19

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