OSPF route manipulation

[tlxbx]

Attached topology. All routers interfaces are part of the same /24 & area 0. 

1.1.1.1/32 is adv. from both R1 & R4. Is there a way I can influence R5 to prefer R1 over R4? 

[MHM Cisco World]

if this Lo is redistribute into OSPF then you can used metric when redistribute.
make metric in R1 prefer than metric in R4. 

[tlxbx]

It's not redistributed but rather by using network statements. 

[MHM Cisco World]

I will check,  will lab it now.

[tlxbx]

Thank you

[MHM Cisco World]

as @Harold Ritter  mention 
I change the cost of Lo 1.1.1.1 in R1 
and R3 select the low cost toward R2 not R1

[balaji.bandi]

is this OSPF configured as point to point or DR and BDR election process ?

you can change the administrative distance or metric to use R1 as prefered.

between R4 and R5 play with cost in the interface - example ip ospf cost 20

[tlxbx]

DR and BDR election.

you can change the administrative distance or metric to use R1 as preferred.

--> How can I do this? Since I only have 1 link that is part of the same broadcast domain. If I change anything it changes for all received prefixes. 

[balaji.bandi]

i have add information

between R4 and R5 play with cost in the interface (including loopback) - example ip ospf cost 20

make sure you select the router-id in ospf if not that will be duplicated.

[Harold Ritter]

Hi @tlxbx ,

You can simply increase the ospf cost for lo0 on R4. This will cause R5 to prefer R1.

R4:

int lo0

ip ospf cost 2 (1 by default)

Regards,

[Joseph W. Doherty]

The one possible issue I see with @Harold Ritter's approach, it could impact other routers (no others in diagram, though) too, i.e. not just R5.

If you really wanted to limit this to just R5, perhaps a distribute-list in might work.  In OSPF distribute-list in only impacts the route table on the router it's applied to.

[tlxbx]

Ah thanks. I will look into distribute-list.

[tlxbx]

Yup..yup that did it. Now is there a way I can influence that from R5 itself?

[Harold Ritter]

Hi @tlxbx ,

You can indeed use a distribute-list to only allow the route coming from R1 to be installed in the RIB on R5, as suggested by @Joseph W. Doherty . The drawback of this method is that if R1 fails, the route via R4 will not be installed, as it is filtered by the distribute-list. So no automatic fall back from R1 to R4 in this case.

Regards, 

[MHM Cisco World]

100% right.
we have little option here since we deal with intra-area ospf.
I have one idea but I must test it first.