OSPF DR/BDR Election
Just to clarify what I think I understand...
The DR is elected by the highest priority code, and BDR is elected by the second highest. In the event of a tie, the highest Router ID wins. If the priority code is set to 0, then the router won't take part in the election.
All this is a little bit irrelevant though as it's not pre-emptive, so in reality the first router that turns on becomes the DR, the second becomes the BDR, and the actual election process will only ever take place if the DR fails - in which case the BDR always becomes the DR and an election takes place to elect a new BDR.
So in real life, it's whichever is powered on / has OSPF enabled first, but if a question came up like "look at these 5 routers, which is the DR and which is the BDR?" in the exam then I'd give the text book answer of highest priority / highest router ID.
Does that sound about right?
The DR is elected by the highest priority code, and BDR is elected by the second highest. In the event of a tie, the highest Router ID wins. If the priority code is set to 0, then the router won't take part in the election.
All this is a little bit irrelevant though as it's not pre-emptive, so in reality the first router that turns on becomes the DR, the second becomes the BDR, and the actual election process will only ever take place if the DR fails - in which case the BDR always becomes the DR and an election takes place to elect a new BDR.
So in real life, it's whichever is powered on / has OSPF enabled first, but if a question came up like "look at these 5 routers, which is the DR and which is the BDR?" in the exam then I'd give the text book answer of highest priority / highest router ID.
Does that sound about right?
Current objective: CCNA Security
My blog: mybraindump.co.uk
My blog: mybraindump.co.uk
Comments
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networker050184
Mod Posts: 11,962 Mod
Sounds about right.An expert is a man who has made all the mistakes which can be made. -
iamme4eva
Member Posts: 272
Thanks networker. I thought I had it, but it helps to have confirmation.
Current objective: CCNA Security
My blog: mybraindump.co.uk -
srg
Member Posts: 140
Yeah on the exams they want to know like if there is a DR/BDR election, who will win? But you're completely right, the router who boots first will have a pretty lonely DR/BDR election and become DR until it drops, or OSPF process is restarted.