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

Marko

if we make the HUB priority 0 then each spoke would see the following in
the election debugs...

Spoke 1
*Mar 1 05:15:25.278: OSPF: Elect BDR 0.0.0.0
*Mar 1 05:15:25.278: OSPF: Elect DR 2.2.2.2
*Mar 1 05:15:25.278: DR: 2.2.2.2 (Id) BDR: none

Spoke 2
*Mar 1 05:15:26.774: OSPF: Elect BDR 0.0.0.0
*Mar 1 05:15:26.774: OSPF: Elect DR 3.3.3.3
*Mar 1 05:15:26.774: DR: 3.3.3.3 (Id) BDR: none

where in fact the HUB see's

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 200 FULL/DR 00:00:33 172.168.18.2 Serial1/0
3.3.3.3 100 2WAY/DROTHER 00:00:35 172.168.18.3 Serial1/0

so each spoke declares themselves as DR but the HUB elects one DR in
precedence of of priority/highest router-id

the non DR/BDR spoke from HUBS perspective goes into a EXSTART and keeps
re-transmitting his DBD packet but stays in a DOWN state

If the HUB remains as DR or BDR then we can get full LSA LSDB replication
from each spoke in this design = NBMA ip ospf network broadcast

Let me know if that's not right..

BR

Tony

On 22 February 2014 01:47, Marko Milivojevic <markom_at_ipexpert.com> wrote:

> Things do get a bit more tricky in hub and spoke configurations when all
> routers don't see all the hellos. Try setting up hub-and-spoke making sure
> hub is NOIT the DR. See what the result will be. Now, ignore for a second
> the fact your routing will be broken, but observe DR/BDR status on the 3
> devices. It's really entertaining!
>
> --
> Marko Milivojevic - CCIE #18427 (SP R&S)
> Senior CCIE Instructor / Managing Partner - iPexpert
> :: Free Video Training: http://youtube.com/iPexpertInc
> :: Social: http://twitter.com/@icemarkom | http://fb.me/ccie18427
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>
>
>
> On Fri, Feb 21, 2014 at 5:41 PM, vishal bhugra <vishal.bhugra_at_gmail.com
> >wrote:
>
> > Thanks Marko and Brian
> >
> > Now I understood the complete election process
> >
> >
> > On Fri, Feb 21, 2014 at 4:28 PM, Marko Milivojevic <markom_at_ipexpert.com
> >wrote:
> >
> >>
> >> 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.
> >>
> >> --
> >> Marko Milivojevic - CCIE #18427 (SP R&S)
> >> Senior CCIE Instructor / Managing Partner - iPexpert
> >> :: Free Video Training: http://youtube.com/iPexpertInc
> >> :: Social: http://twitter.com/@icemarkom | http://fb.me/ccie18427
> >> :: iPexpert: http://www.ipexpert.com/Communities | +1-810-326-1444
> >>
> >>
> >>
> >> 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
> >>> >
> >>> >
> >>> > Blogs and organic groups at http://www.ccie.net
> >>> >
> >>> >
> _______________________________________________________________________
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> >>> >
> >>> >
> >>> >
> >>> >
> >>> >
> >>> >
> >>> >
> >>> >
> >>>
> >>>
> >>> --
> >>> Thanks&regards
> >>>
> >>> Vishal
> >>> +91 8587900305
> >>>
> >>> Best way to predict the future ..... is to create it
> >>> _______________________________________________
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> >>>
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> >>>
> >>
> >>
> >
> >
> > --
> > Thanks&regards
> >
> > Vishal
> > +91 8587900305
> >
> > Best way to predict the future ..... is to create it
> >
> _______________________________________________
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>
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Received on Sat Feb 22 2014 - 16:56:52 ART