Re: [OSL | CCIE_RS] OSPF DR and BDR election

During the WAIT state (dead-interval duration), all routers will be sending
hellos with DR/BDR set to 0.0.0.0. However, all routers can see each
other's hellos and since noone is claiming DR/BDR they will hold the
election - basically. each router will decide what's going to be the
topology based on hellos they've observed. One that is at that time
considered the best will claim DR and the second best will claim BDR.
That's how they will populate the fields once they leave the WAIT state.

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On Fri, Feb 21, 2014 at 3:58 PM, vishal bhugra <vishal.bhugra_at_gmail.com>wrote:
> 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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> >
> >
> >
> >
> >
>
>
> --
> Thanks&regards
>
> Vishal
> +91 8587900305
>
> Best way to predict the future ..... is to create it
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