Re: OSPF DR and BDR election

Hello Brian

Thanks for your kind answer.

If I configure 5 routers on broadcast network, all with same priority. They
all are new in the segment and now the election start. Now my questions
are:-

1) Do all of them put their Router ID in DR field of Hello? and highest RID
will become the DR and lower one will be the BDR ?

                                                                   OR

2) Will some one put his router ID in BDR field ? and if yes how will he
decide that it has to put the RID in BDR field of Hello packet and not the
DR.

On Fri, Feb 21, 2014 at 2:28 PM, Brian McGahan <bmcgahan_at_ine.com> wrote:

> In general the first router to join the segment becomes DR and the second
> router to join becomes BDR. If DR fails the BDR is promoted to DR and there
> is a new election for BDR. There are some odd corner cases where this wont
> happen though.
>
> When the router joins the segment it listens for WAIT timer to expire. If
> during this interval it receives a hello from another router on the
> segment, it will accept the DR information in the packet and start to send
> hellos. If however no one is heard during WAIT, the router elects itself DR
> and inserts this in its own hello.
>
> This mean that if for some reason communication is broken during WAIT
> interval, two routers can elect themselves as both DR, in which case there
> *will* be a preemptive election once they both hear each others hellos.
>
> For example this could happen if your OSPF DEAD/WAIT interval is lower
> than your STP Forward Delay, WAIT would expire before the router can
> receive packets and it would elect itself as DR.
>
> This is not the normal case though. For more info see
> https://tools.ietf.org/html/rfc2328#page-75
>
>
> Brian McGahan, 4 x CCIE #8593 (R&S/SP/SC/DC), CCDE #2013::13
> bmcgahan_at_INE.com
>
> Internetwork Expert, Inc.
> http://www.INE.com <http://www.ine.com/>
>
> On Feb 21, 2014, at 6:01 AM, "Carlos G Mendioroz" <tron_at_huapi.ba.ar>
> wrote:
>
> I don't know where are you reading this, but I thought that there is
> only BDR election process. Once you are BDR, then you can jump to DR if
> the current DR fails.
>
> So that is why, I guess. You don't opt, you have no choice :)
> -Carlos
>
> vishal bhugra @ 20/02/2014 20:28 -0300 dixit:
>
> Hello Experts
>
>
> While going through the DR and BDR election process. I gone through a line
>
> wherein during the process of election the router will segregate the list
>
> of routers who have mentioned themselves as BDR and those who have
>
> mentioned themselves as DR.
>
>
> After segregation out of the list of BDR, the elected BDR will be with the
>
> highest priority and if not then highest Router ID.
>
>
> Now my question is .. Why would a router will opt himself for BDR and not
>
> for DR. Or we can say how a router will come to conclusion that it has to
>
> go for be a BDR not the DR.
>
>
>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>
>
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Vishal
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