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OSPF, VLANs and reconvergence


I have an OSR with several routers connecting back to it via gig interfaces. All the routers are on the same subnet/VLAN and the OSR has a VLAN interface, again on the same subnet.

The routers and OSR are all running OSPF and using a loopback for the router ID. The rest of the OSPF config is default so there are no priorities set on the links to choose the DR/BDR. Once the network is settled and the DR/ BDR determind everything runs smoothly until a new router is connected to the OSR.

The loopback on the new router is higher than those currently configured on the other routers and when I open up the interface on the OSR OSPF starts a complete re-calculation and a new DR/BDR is elected. The new router then becomes the new DR.

My understanding was a new DR would not be re-elected until the DR goes down and then the BDR will be promoted and another BDR selected.

I can get around the problem by putting the new router on the network without any OSPF config, opening up the interfaces first and then adding the OSPF config.

Is this just a quirk of using VLANs, OSPF and the OSR as an 'aggregation' point?

Many thanks in advance for any help.


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