Solved: choosing the designated router

fran19422 · ‎08-11-2012

Hello, if I was manually selecting which router would be the designated router, I would look for:

- the router with highest capacity

- the router in the most central location

Are there any other criteria that people use for selecting which router would be most suitable as the designated router ?

Thanks for any help.

Peter Paluch · ‎08-11-2012

Hi Philip,

I assume you are talking about OSPF Designated Router. In that case, the only criteria for me would be the stability of this router - i.e. UPS, stable IOS, proven stable platform, etc. No other criteria would mean anything to me - note that in particular respect to the capacity of this router, it is irrelevant: all routers in a single area must have their link-state databases synchronized and thus identical. The load on the DR and other routers is practically the same. As the DR is responsible for representing a multiaccess network in the link-state database, it is strongly recommended to make this router as stable and long-lived as possible (this is also the reason why DR/BDR elections are non-preemptive - to increase the stability and prevent unnecessary link-state database changes).

Also please note that a DR is elected per each multiaccess segment, not one for the entire area. If your OSPF area consists of, say, 10 distinct Ethernet networks then each of them is going to have its own DR, resulting in 10 DRs in your area. With this in mind, you surely agree that it is impossible to have all 10 DRs "as central as possible".

Best regards,

Peter

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Peter Paluch · ‎08-11-2012

Hi Philip,

I assume you are talking about OSPF Designated Router. In that case, the only criteria for me would be the stability of this router - i.e. UPS, stable IOS, proven stable platform, etc. No other criteria would mean anything to me - note that in particular respect to the capacity of this router, it is irrelevant: all routers in a single area must have their link-state databases synchronized and thus identical. The load on the DR and other routers is practically the same. As the DR is responsible for representing a multiaccess network in the link-state database, it is strongly recommended to make this router as stable and long-lived as possible (this is also the reason why DR/BDR elections are non-preemptive - to increase the stability and prevent unnecessary link-state database changes).

Also please note that a DR is elected per each multiaccess segment, not one for the entire area. If your OSPF area consists of, say, 10 distinct Ethernet networks then each of them is going to have its own DR, resulting in 10 DRs in your area. With this in mind, you surely agree that it is impossible to have all 10 DRs "as central as possible".

Best regards,

Peter