OSPF path selection

[Donia]

Hello 

I have a problem that i am receiving prefix on a router with ospf from 2 direction ( primary/ backup ) devices and it should be preferred using metric in the redistribution statement as below

the problem that the metric isn't seen in the router and load balancing is done and i don't know why it is happening

R3#sh ip route ospf | s 10.0.0.0 
10.0.0.0/8 is variably subnetted, 34 subnets, 8 masks
O E2 10.0.0.0/8 [110/2] via R1, 05:20:52, GigabitEthernet2/0/0
                          [110/2] via R2, 7w0d, GigabitEthernet1/0/0

R1 configuration 

router ospf 1

summary-address 10.0.0.0 255.0.0.0
summary-address 172.16.0.0 255.240.0.0
summary-address 192.168.0.0 255.255.0.0 

redistribute bgp AS metric 200 subnets route-map TO-OSPF

route-map TO-OSPF permit 10
match ip address prefix-list TO-OSPF

ip prefix-list TO-OSPF seq 5 permit 10.0.0.0/8 le 32
ip prefix-list TO-OSPF seq 10 permit 172.16.0.0/12 le 32
ip prefix-list TO-OSPF seq 15 permit 192.168.0.0/16 le 32

R2 Configuration:

router ospf 1

summary-address 10.0.0.0 255.0.0.0
summary-address 172.16.0.0 255.240.0.0
summary-address 192.168.0.0 255.255.0.0

redistribute bgp AS metric 100 subnets route-map TO-OSPF

route-map TO-OSPF permit 10
match ip address prefix-list TO-OSPF

ip prefix-list TO-OSPF seq 5 permit 10.0.0.0/8 le 32
ip prefix-list TO-OSPF seq 10 permit 172.16.0.0/12 le 32
ip prefix-list TO-OSPF seq 15 permit 192.168.0.0/16 le 32

from the above configuration R3 should prefer route from R2  which has metric 100 but it isn't the result i got from R3

however if i check another subnet like 192.168.0.0

R3#sh ip route ospf | s 192.168.0.0

O E2 192.168.0.0/16 [110/100] via R2, 6w6d, GigabitEthernet1/0/0

can anyone tell me why the metric is changed on subnet 10.0.0.0 however it is ok for subnet 192.168.0.0

[Harold Ritter · Accepted solution]

Hi @Donia  ,

The fact that you are seeing the metric 2 instead of the metric 100 or 200 for the 10/8 summary route is due to the fact that you are redistributing from multiple sources (bgp and ospf 2). The lower metric coming from ospf 2 is used instead of the metric 100/200 from the

redistribute bgp

statements.

Regards,

[Donia]

yes i tried to check another prefixes that should be learnt from the other ospf Process and found the same behavior that load balancing is done so i will need to make change on the redistribute ospf 2 to take the same metric as

redistribute bgp

[Kanan Huseynli · Accepted solution]

Hi,

there will not be LSA for subset routes in OSPF DB of process 1, because you do summarization (you have only summary route LSA in DB).

route-map NETWORKS doesn't have 10.0.0.0/8 as an entry but other 10.x.x.x/18 le 32

So, it is possible that routes from this route-map is considered in summarization. Check routes in OSPF process 2 rib:

show ip ospf 2 rib | inc 10.

[MHM Cisco World]

you network like below 
the R2 and R3 have eBGP to R4
R4 inject 10.0.0.0/8 le 32 into R2 and R3 
R2 and R3 redistribute it into OSPF  
then you summary the 10.0.0.0/8 le 32 to 10.0.0.0/8  ?
am I right ?

[MHM Cisco World]

Routing Bit Set on this LSA in topology Base with MTID 0 <<- all route external dont have this bit 
can you confirm that and still use the topology 

[Donia]

these routes should be external but 10.0.0.0/8 seems to have a problem due to the other redistribute ospf 2 as i checked another prefix inside ospf 2  in the route map Network and found it in R3 seen from 2 paths ( the same behavior 10.0.0.0/8)

if you checked again 192.168.0.0/16  ( sh ip ospf database 192.168.0.0 ) that i sent it before MTID =0 and it has the same metric 100 which i have added to all

redistribute bgp route

[MHM Cisco World]

OSPF2 !!
where is OSPF2. I see only one OSPF which is OSPF 1?
can you more elaborate ?

[MHM Cisco World]

I already try config and it right 
the eBGP advertise the 5.0.0.0/16 and the

OSPF redistribute bgp 

and set metric to 200
and result is 
5.0.0.0/8 with metric 200
I think there is something else here

[MHM Cisco World]

you share this before all 10.x.x.x is learn from eBGP 
so the summary use it as seed of summary address 
the metric is all same equal 0 

O 10.0.0.0/8 is a summary, 3d17h, Null0
B 10.0.152.158/32 [20/0] via PE, 02:03:33
B 10.2.0.0/16 [20/0] via PE, 02:03:33
B 10.1.153.152/30 [20/0] via PE, 02:03:33
B 10.1.153.232/30 [20/0] via PE, 02:03:33
B 10.1.54.152/30 [20/0] via PE, 02:03:33
B 10.1.54.232/30 [20/0] via PE, 02:03:33

so only remove summary and add it again 
if you can 
thanks