OSPF masters

Unanswered Question
Jun 21st, 2008


How may master routers will be in a network if there are 3 routers connected serialy.

I have this problem too.
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Overall Rating: 5 (1 ratings)
Richard Burts Sun, 06/22/2008 - 00:08

Perhaps we have a semantic issue, but I am not clear what you mean when you talk about OSPF master router. "Master Router" is not a common OSPF term.

Did you perhaps mean Designated Router (DR and BDR)? If the routers are connected by serial interfaces then there are no DRs on serial interfaces. If there are Ethernet interfaces then there will be 1 DR for each Ethernet segment in the OSPF network (and perhaps 1 BDR for each Ethernet segment).

If your question was not about DR and BDR then perhaps you can clarify your question?



drnteam Sun, 06/22/2008 - 00:54


My question is not related to DR. When the time of DD packet exchnage one of the router will become the master.My question is how many masters will be there if R1 is connected to R2 and R2 is connected to R3.

jamesl0112 Sun, 06/22/2008 - 00:37

Assuming that you are referring to the OSPF DR and BDR, then there will not be an election if the OSPF network type is point-to-point or point-to-multipoint. However, there will be an election if the network type is non-broadcast (e.g. frame relay) or broadcast.

You can check the OSPF network type with show ip ospf interface, and you can check the router state with show ip ospf neighbor.

Richard Burts Sun, 06/22/2008 - 00:51

The distinction that James makes about the election of DR and BDR depending on OSPF interface type is a more accurate distinction than my generalization about no DR on serial and DR on Ethernet. I appreciate his clarification and have rated it.



jamesl0112 Sun, 06/22/2008 - 01:17


Thanks for the points!


I think you might be referring to the master/slave relationship routers establish in the exstart state. This happens after the DR/BDR election process (if applicable). The router with the highest RID becomes the master and starts the exchange.

So, assuming that this is your actual question - the answer is that this master/slave election is on a per-neighbor basis.


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