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? 

[Harold Ritter]

Hi @tlxbx ,

You are absolutely right. The revised access-list is the proper way to go. 

Regards,

[Joseph W. Doherty]

Perhaps:

route-map test deny 10
match ip address prefix-list prefix1
match ip next-hop prefix-list nh1
route-map test permit 20

!or

route-map test permit 10
match ip address prefix-list prefix1
match ip next-hop prefix-list nh1
set metric 32000
route-map test permit 20

The latter possibly supporting the "auto" fail-over @Harold Ritter suggested as a good thing (which often it is).

[tlxbx]

Tried below & nothing changed. 

route-map test permit 10

ip prefix-list nh1 seq 5 permit 192.168.0.1/32
!
ip prefix-list prefix1 seq 5 permit 1.1.1.1/32
!
route-map test permit 10
match ip address prefix-list prefix1
match ip next-hop prefix-list nh1
set metric 32000
!
route-map test permit 20

router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
distribute-list route-map test in

**********

R5#sh ip route os
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/2] via 192.168.0.4, 00:00:01, FastEthernet0/0
                 [110/2] via 192.168.0.1, 00:00:01, FastEthernet0/0

[Joseph W. Doherty]

Did you try first alternative?

PS:

I.e.:

route-map test deny 10
match ip address prefix-list prefix1
match ip next-hop prefix-list nh1
route-map test permit 20

[Harold Ritter]

Hi @Joseph W. Doherty ,

Option 2 would have been a good idea, but the "distribute-list with route-map" feature doesn't allow to change anything on the route. Only the match statement will be taken in consideration. The set statement will be ignored.

Regards,

[Joseph W. Doherty]

BTW, found this "working [?] example" of using a "set" with an OSPF distribute-lise: https://docs.ruckuswireless.com/fastiron/08.0.60/fastiron-08060-l3guide/GUID-EB1339A2-5DCB-41D0-A215-F3A9D69174D9.html

[Harold Ritter]

Hi @Joseph W. Doherty , 

It definitely looks like IOS, but it is not. FastIron is an NOS from Ruckus, which is a competitor.

Regards,

[Harold Ritter]

I completely agree @Joseph W. Doherty . Sometimes the solution might be cumbersome than the problem itself.

Regards,

[tlxbx]

Thank you both for your input. I'd still like to complete it at least in a lab environment. If nothing else it will solidify my  OSPF understanding  

[MHM Cisco World]

we can play with cost in two case 
P2P 
P2M 

here we have broadcast, so only we change the network type to P2M to solve the problem 

then 

neighbor x.x.x.x cost <value>

this make R3 prefer either R1 or R2 for prefix Lo 1.1.1.1

[tlxbx]

Thank you. Can you do a lab with distribute-list as it didn't work for me?

It would look something like the following:

route-map test permit 10
match ip address prefix-list prefix1
match ip next-hop prefix-list nh1
!
ip prefix-list nh1 seq 5 permit <nexthop to R1>
ip prefix-list prefix1 seq 5 permit 1.1.1.1/32
!
router ospf xxx
distribute-list route-map test in

Regards,

Harold Ritter
Sr Technical Leader

[MHM Cisco World]

I am out now, but from my experience distrubte-list not work at all for this case , as @Harold Ritter mention before.

[Harold Ritter]

Hi @tlxbx ,

Have you been able to test the following configuration, which might be compatible with the IOS version you run.

access-list 199 permit ip host 192.168.0.1 host 1.1.1.1
router ospf 1
distribute-list 199 in

Regards