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

Yes that's right. If the hub isn't the DR then the database won't be synced. This applies to legacy hub and spoke like Frame Relay/ATM but also to logical hub and spoke like DMVPN.

Brian McGahan, 4 x CCIE #8593 (R&S/SP/SC/DC), CCDE #2013::13
bmcgahan_at_INE.com<mailto:bmcgahan_at_INE.com>

Internetwork Expert, Inc.
http://www.INE.com<http://www.ine.com/>

On Feb 22, 2014, at 11:57 AM, "Tony Singh" <mothafungla_at_gmail.com<mailto:mothafungla_at_gmail.com>> wrote:

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<mailto: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
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On Fri, Feb 21, 2014 at 5:41 PM, vishal bhugra <vishal.bhugra_at_gmail.com<mailto: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<mailto: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<tel:%2B1-810-326-1444>
>>
>>
>>
>> On Fri, Feb 21, 2014 at 3:58 PM, vishal bhugra <vishal.bhugra_at_gmail.com<mailto: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<mailto: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<mailto: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<mailto: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<mailto:tron_at_huapi.ba.ar>>  LW7 EQI  Argentina
>>> >
>>> >
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>>> >
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>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>>
>>>
>>> --
>>> Thanks&regards
>>>
>>> Vishal
>>> +91 8587900305<tel:%2B91%208587900305>
>>>
>>> Best way to predict the future ..... is to create it
>>> _______________________________________________
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>>
>>
>
>
> --
> Thanks&regards
>
> Vishal
> +91 8587900305<tel:%2B91%208587900305>
>
> Best way to predict the future ..... is to create it
>