Re: OSPF understanding

Yay!
Getting a commendation from one of my mentors.
Thanks:)

On Sat, Feb 13, 2010 at 5:48 PM, Jared Scrivener
<lists_at_jaredscrivener.com>wrote:

> Bobola, yours is a great explanation - it gets straight to the point which
> is that if the TTL is 1 and the hops needed are 2 then the OSPF packet won't
> make it to the supposed DR. Well done.
>
> --
> Cheers,
>
> Jared Scrivener
> CCSI #30878, CCIE3 #16983 (R&S, SP, Security)
> www.MicronicsTraining.com
> Sr. Technical Instructor
>
> YES! We take Cisco Learning Credits!
> Training And Remote Racks available
>
> LinkedIn:www.linkedin.com/in/jaredscrivener
>
>
> On Fri, Feb 12, 2010 at 7:32 AM, Bobola Oke <okebobola_at_gmail.com> wrote:
>
>> Hi Nadeem,
>>
>> I don't think you should look at this as a 224.0.0.6 thing... But if it
>> helps you understand...
>>
>> OSPF hellos are sent with a TTL of 1. R5 would not forward any hello to
>> R4.
>> So therefore you wont have more than one neighbor on all the routers
>> except
>> for the hub which would have 4 neighbors, right?
>>
>> This explains why R5 can chose R4 as the DR, all other routers which are
>> not
>> even aware of R4 as a nieghbor in the first instance cannot possibly use
>> it
>> (R4) as the DR or even BDR. As far as R1 - R4 are concerned, the only
>> ospf
>> neighbor they have is R5.
>>
>> I'm sure other GS members would be able to explain better though...
>>
>>
>>
>> HTH
>>
>> Bobola
>>
>>
>>
>> On Thu, Feb 11, 2010 at 9:14 PM, Nadeem Rafi <nrafia_at_gmail.com> wrote:
>>
>> > Thanks for input...
>> >
>> > I know, this is bad design and the reason is also obvious as you stated.
>> > But i am interested in how this is happening in back end. As i stated
>> > before, DR/BDR is property of a interface, an interface can be only
>> DR/BDR
>> > for an interface/segment. Then how it come can be DR/BDR at the same
>> time?
>> > Please can you shed some light on how 224.0.0.6 address is
>> > announced/selected?
>> >
>> >
>> >
>> > On Thu, Feb 11, 2010 at 11:51 PM, Bobola Oke <okebobola_at_gmail.com>
>> wrote:
>> >
>> >> Hi Nadeem,
>> >> This is a frame relay thing....
>> >>
>> >> The other routers cannot connect to R4 on layer2 so they use the only
>> >> available mapping they've got which is R5
>> >>
>> >> They can only get to R4 when ospf is already running and they need a DR
>> to
>> >> do so which has to be R5. But R5 has a mapping to R4 so it can use that
>> as
>> >> its own DR. Hope you understand this.
>> >>
>> >> In real life, this is bad network design though. When running hub and
>> >> spoke, you only want your hub to be DR.
>> >>
>> >> HTH
>> >>
>> >> Bobola Oke
>> >>
>> >>
>> >>
>> >> On Thu, Feb 11, 2010 at 7:49 PM, Nadeem Rafi <nrafia_at_gmail.com> wrote:
>> >>
>> >>> Hi GS,
>> >>>
>> >>> working with OSPF HUB and spoke, R5 being hub, R1 - R4 being spokes
>> >>> (using
>> >>> non-broadcast network type, all routers using physical interfaces).
>> >>> Spokes
>> >>> dont have direct frame-relay mappings with each other, but through
>> hub.
>> >>> Made
>> >>> some experimental changes in this way.
>> >>>
>> >>> 1- make R5 DR by using priority
>> >>> 2- R1-R3 set ip ospf priority 0
>> >>> 3- R4 set priority lower than R5 but non 0.
>> >>>
>> >>> R5 becomes DR and R4 BDR, every thing works fine, other three spokes
>> get
>> >>> R5
>> >>> as DR.
>> >>>
>> >>> Now cleared the R5 OSPF Process and R4 Become DR and R5 elected as
>> BDR.
>> >>> Vriefied both on R4 and R5 by show ip ospf int command.
>> >>>
>> >>> BUT , other three spokes, R1-3 are still identifying R5 ad DR. Why? As
>> >>> for
>> >>> as i know, DR/BDR is proprty of interface not router. When R5 is BDR
>> with
>> >>> R4
>> >>> on same interface then how come it can be DR for other routers on same
>> >>> interface?
>> >>> Interestingly, Database identifies correct DR, but show ip ospf
>> neighour
>> >>> command don't reflect it correctly.
>> >>>
>> >>> Any input will be of great value.
>> >>>
>> >>> Best Regards,
>> >>>
>> >>> Nadeem Rafi
>> >>>
>> >>>
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>> >>>
>> >>>
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Received on Sat Feb 13 2010 - 22:49:24 ART