OSPF Master/Slave lection in an already converged OSPF network

[venumavila]

Hello OSPF Experts,

   I have question on OSPF Master/Slave election in an already converged network, referred multiple sources still not able to get a clear answer.

I have a converged OSPF network with DR/BDR all already elected and has some number of various types of LSAs.in the network

Now I am connecting in a brand new Router to the above network.

In this scenario, the new Router has higher router ID.

1) So during the neighborship formation, will this new router become Master because of its higher router Id ? eventhough there is already a DR and BDR in the network.

2) Some sources say that, when a new router is being introduced to a network where there is already a DR and BDR, the DR is always going to become Master, irrespective of Router ID or new router, is this correct ??

3) If this new Router becomes Master, and it initiates LS DB exchange with 0 LSAs, will this new router will wipe out already existing LSAs in the connecting converged OSPF Routers ? If not how is this taken care.

It would be great if someone can clarify this.

Thanks,

mavila

[Jon Marshall]

Mavila

If there is already a DR and BDR on that network then adding the new router will not change that ie. even though the new router has a higher priority it will not become either the DR or BDR because there is no new election.

So the new router will simply form adjacencies with the existing DR and BDR and subsequently get a copy of the existing LSA database.

Jon

[venumavila]

Thanks Jon for your reply.

I still have confusion over the Master slave election. The DR/BDR election is clear. it won't get disturbed in a converged network.

But when the new router is introduced into the converged network (where DR/BDR is already there), in the Exstart/Exchange phase of neighborship formation, can the new router become Master or will it will be always slave ?.

If the new router becomes Master, will it going to overwrite the LSAs in the converged network ?

thanks

Mavila.

[Jon Marshall]

Mavila

I see what you are asking now. My apologies for misunderstanding the question.

As far as I know the DR could indeed become the slave if it has a lower priority but that doesn't mean the LSA database will be overwritten.

What happens is that each router will describe their own link state databases to each other using the headers of the LSAs. If either router sees an LSA that is not in it's own database or sees a more recent copy of that LSA being advertised it then requests the full LSA from the other router.

The new router will have an empty LSA database and so will request all the full LSAs from the DR. The DR will not receive any LSA headers from the new router so won't request anything.

So it doesn't really matter which router is the slave and which is the master and it certainly wouldn't mean the DR would have it's own LSA database overwritten.

Jon