Unanswered Question
Oct 12th, 2007

How should elect the DR/BDR in the attached network. All connected interfaces are on different /29 network.

1. R1-Sw1 = x.x.x.0/29

2. R2-Sw2 = x.x.x.16/29

3. SW1-SW2 = x.x.x.24/29

all are configured as AREA0 and wanted R1 as DR and R2 as BDR.It involves redistribution of BGP to OSPF anf vice-versa.

Please share the workaround.

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Edison Ortiz Fri, 10/12/2007 - 10:21

R1 and R2 won't be neighbors.

R1 will only be neighbor with SW1 and R2 will only be neighbor with SW2.

They need to share the same segment for the DR/BDR to occur.

gaurav_thapar79 Fri, 10/12/2007 - 10:29

Hi edison,

Please suggest the workaround to achieve the requirement. Will virtual link server the requirement being in same AREA0?

please share your comments.

Edison Ortiz Fri, 10/12/2007 - 10:40

A workaround for what ?

Looking at your diagram and your post, doesn't tell me much.

Ideally, you would want R1 and R2 to be the DR for their respective segment, but you will also have to deal with the SW1 and SW2 segment DR/BDR election.

Since you only have point-to-point links between devices, according to the diagram, just configure ip ospf network point-to-point under the OSPF interfaces and you don't have to worry about the DR/BDR election.

gaurav_thapar79 Fri, 10/12/2007 - 11:23

Dear Edison,

Please have a look at attached diagram which states complete requirement. With above stated information, would we be able to achieve BDR requirement at R2.please share then how would sh ip ospf database and type of routes look like?

currently all learned routes appears to be Type-2 External at both R1 nad R2 routers.

Edison Ortiz Fri, 10/12/2007 - 12:25

Comment from your PowerPoint file:

R1 Router should be DR on segment and while R2 Router should be the BDR

Well, I don't see on any of these files that segment. However, you can force DR assignment by entering the highest numeric value in the router-id, for instance:

router ospf 1


But they need to share the same IP subnet and be neighbors for it to work. Based on your diagrams, they aren't neighbors.


You aren't giving me much to work with here.

I need you to be more thorough in your next post as we aren't going anywhere.

GillieLucent Fri, 10/12/2007 - 11:24


If you want a work around, you need to do following :

1. All R1,R2,SW1 and SW2 should be in same /29 network

2. There should be connection between R1 and R2

3. Assign highest router-id to R1

4. Configure priority zero to SW1 and Sw2.

Virtual link can be used to repair partitioned area 0, but that should not used as permanent solution.




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