OSPF over Frame-relay

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Mar 4th, 2009
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hi this question i found it in a website for CCIE ospf over FR as bellwo


Configure OSPF on R4,R5,R6. Do not use the neighbor statement to get the adjacencies up. Ensure that R6 is always the DR


as long as they want r6 to be the DR then we canyt use network point to point over point to multipoint

but the strange thing is also asked to NOT use neighbor ??

and idea !!


thank you

Correct Answer by Giuseppe Larosa about 8 years 4 months ago

Hello Marwan,

I think you should build a full mesh of PVCs with static mapping with broadcast option

+

frame-relay map ip x.x.x.1 101 broadcast

frame-relay map ip x.x.x.2 102 broadcast


+

ip ospf network broadcast


in this way you don't need the neighbor commands but this requires multicast support that for FR is treated like broadcast


or you can use


point-to-multipoint on hub

point-to-point on each spoke



RFC 2328 provides point-to-multitpoint mode


you need also to provide R6 with an higher OSPF priority on the link to be sure it is elected DR on segment


no neighbors commands => multicast discovery and DR election occurs


Hope to help

Giuseppe


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Correct Answer
Giuseppe Larosa Wed, 03/04/2009 - 13:47
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Hello Marwan,

I think you should build a full mesh of PVCs with static mapping with broadcast option

+

frame-relay map ip x.x.x.1 101 broadcast

frame-relay map ip x.x.x.2 102 broadcast


+

ip ospf network broadcast


in this way you don't need the neighbor commands but this requires multicast support that for FR is treated like broadcast


or you can use


point-to-multipoint on hub

point-to-point on each spoke



RFC 2328 provides point-to-multitpoint mode


you need also to provide R6 with an higher OSPF priority on the link to be sure it is elected DR on segment


no neighbors commands => multicast discovery and DR election occurs


Hope to help

Giuseppe


Edison Ortiz Wed, 03/04/2009 - 14:15
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you need also to provide R6 with an higher OSPF priority on the link to be sure it is elected DR on segment


I prefer going with 'priority 0' on R4 and R5 since OSPF DR role can't be preempted. If R4 or R5 boot up first, even having a higher priority on R6 won't do any good.


__


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Marwan ALshawi Wed, 03/04/2009 - 15:09
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Ok thanks for both of you guys


ok, Giuseppe


if i do tow maps with broadcast keyword on each of the hub, and spoks


now what ospf interfacce network type i have to chose to make it work without the neighbor command ?


for point to multi point on the hub

and point to point on the spokes

i am prety sure will work but it NEED to alter the timers on the hub or the spokes to make it the same !!


But the question here if i do it like this will be any DR BDR in this CASE ??


Thanks again guys


because every time i feel ok with ospf network types over FR then i find somthing confuse me again :)



Edison Ortiz Wed, 03/04/2009 - 15:43
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You need to understand which OSPF Network Type uses the DR/BDR mechanism and which don't.


Based on those findings, then you need to identify which can be used with a neighbor command and which don't.


Since you are preparing for your CCIE, I recommend you hit the documentation and play around in the lab to see the behavior I mention above.


Giuseppe already told you which network type to use but I recommend you play around with all network types and observe what unique behavior each of them exhibits. Until you don't feel comfortable with it, I don't recommend taking a stab to the lab - else it will be a very expensive lunch.


__


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Marwan ALshawi Wed, 03/04/2009 - 15:50
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Hi Edison

thanks for this advice


actually i'm aware about these types but still confuseing sometimes


for example Giuseppe said we could use point to multipoint with p2p on spokes

it is possible and just we need to make the timers on the interaces the same

but also i know these tow network types dos enot use DR BDR now how we can use it in regard to the question above ?


also i asked for broadcast keywork i need to make sure if we have the broadcast keyword in the FR map and we did not change the default interface entwork type which is non-broadcast will this work if not what is the alternative ?


thanks again guys

Edison Ortiz Wed, 03/04/2009 - 16:02
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Yes, it is possible to mix and match the following OSPF network types:


p2p and p2mp

br and non-br


You need to match the timers and you are set.


Your initial question requires the use of the DR and p2p and p2mp do not rely on DR, so what are your options?


The broadcast keyword in the FR is to carry the multicast packets used on routing protocols. Your initial question did not related to this subject at all.



__


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Marwan ALshawi Wed, 03/04/2009 - 16:34
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hi guys

i just solved it

i used tow fram relay maps on each router with broadcast keyword

then i made the interface ospf network type as broadcast

and the hub made as DR by changing the spokes osp priority to 0


by the way sopkes p2p with hub point to multipoint worked after chenging the timers as i mentiioned abive


BUT no DR or BDR then not the right otion for this question


thanks guys for you help

Giuseppe Larosa Wed, 03/04/2009 - 22:48
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Hello Marwan,

I'm sorry if I've caused some confusion but actually as Edison said during preparation you need to play with all possible combinations to see what elements are needed to build a working solution that respects the requirements.


I agree that is wise to give ip ospf priority 0 to spokes.


So you have seen that both solutions don't need neighbor commands but one the point-to-multipoint + p-t-p don't involve DR election.


Hope to help

Giuseppe


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