OSPF Cost Tweaking in BMA Topology

Unanswered Question
Jul 15th, 2010


I have thesse 4 OSPF routers connected as below , with SVI interface forming the neighbors in BMA topology

R1____________100 Mbps____________R2

|                                                              |

|                                                              |

| 600 Mbps                                               |  45 Mbps

|                                                              |

|                                                              |


                     45 Mbps

following is the config on each router

int vlan 653

ip address 192.168.1.x

router ospf 100

network 192.168.1.x area 0

Now , i want Router R4 to choose the path R4-R2-R1 to reach R1, and backup path should be R4-R3-R1.

How can i tune the cost under vlan interface ( SVI ) ? Not sure whether route maps are gonna do the trick !!!

I have this problem too.
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satish_zanjurne Thu, 07/15/2010 - 23:19

I guess handout diagram, does not reflect it properly there is direct link between R2 & R4.

Giuseppe Larosa Sun, 07/18/2010 - 13:05

Hello Satish,

if all devices are connected in a single broadcast domain / IP subnet as your drawing and your network configuration suggests each router would use the neighbor directly to reach IP subnets behind each router.

The only way to enforce a per neighbor cost that could be useful if two routers advertise the same subnet is to use

ip ospf network poin-to-multipoint non-broadcast 

(note cisco proprietary) that would allow to specify per neighbor cost in the router ospf process

However, the best way would be to review design and to implement point-to-point links if possible.

Hope to help



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