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New Member

How to config OSPF on this case?

My network top is here.

R1---------R2

| |

|----R3---|

R1 & R2 is ospf eare 0, R3 is eare 1.

If the link between R1 & R2 is down. The communication of R1 & R2 should be down.

How can I resolve this problem ?

floating routes? or other solution?

10 REPLIES
Cisco Employee

Re: How to config OSPF on this case?

Are there only these 3 routers? If so, I wouldn't even bother to run more than one area and would put all routers in area 0.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Re: How to config OSPF on this case?

are you talking about something like virtual link:http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801ec9ee.shtml

regards

Devang

Re: How to config OSPF on this case?

Devang,

It is posted in the question that R1 and R2 are in area 0 and the R3 is in area 1. We dont have any other area. Virtual link cannot be used here .Virtual link is used to connect an area which is not directly to backbone area through a transit area directly to backbone area.

-amit singh

New Member

Re: How to config OSPF on this case?

In this situation without a connection from R3 to R2 and the link is down between R1 & R2 , R2 will not be able to learn routes and looks to be virtually isolated from the network. In the scenario laid out, only a link between R3 & R2 would guarentee communication.

Cisco Employee

Re: How to config OSPF on this case?

Amit,

Virtual links can also be used to repair a partioned backbone area.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: How to config OSPF on this case?

Thank you for your reply.

I have a question. Virtual link could resolve the problem when the link between R1 & R2 is down. But if the link is work normally, and the virutal link is configed. Whether it work well?

I want it work automatic when the link is down.

Cisco Employee

Re: How to config OSPF on this case?

The cost of the virtual link would be equal to the cost of the shortest path through area 1 (r1-r3+r3-r2).

So under normal circumstances, the direct link between between r1 and r2 would be used for the backbone area intra-area trafic, assuming all link costs are the same.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Re: How to config OSPF on this case?

hi amit,

i think we can connect the partitioned area using the virtual link also...

regards

Devang

New Member

Re: How to config OSPF on this case?

The virtual link could connect the partioned area 0 as long as there was a physical link between r2 & r3. In the provided config drawing it looks like there is no link between r2 & r3. If that is the case then a virtual link could not be configured and communication would be down between r1 & r2.

Silver

Re: How to config OSPF on this case?

My Suggestion is to set all routers in one area which is area0. It is three routers in the end and using other area won't be of much routing improvment.

Regards,

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