OSPF - Problem with Static routes redistributed between processes

[chrisc100]

Hello
I have 4 devices connected as shown in the diagram.

RTRA runs OSPF processes 1+2 for each domain.

I am testing redistribution static routes between domain 2->1, I added a static route in RTRB 9.9.9.9 and added "redistribution static subnets" to ospf process 2.

This works and RTRC can see the route.

However if I add a static route on RTRA and add the same for OSPF process 2 (example 8.8.8.8), the route is not redistributed to OSPF process 1 and RTRC cannot see it.

In order for this to work I need to add "redistribute static subnets" to OSPF process 1.

Is there a reason why this does not work, i.e. a restriction or some documentation/best practice about it?

Thanks in advance.

Relevant configs:

RTRC#show run | se route
router ospf 1
network 192.168.10.0 0.0.0.255 area 0

RTRA#show run | se route
router ospf 1
redistribute ospf 2 subnets
network 192.168.10.0 0.0.0.255 area 0

router ospf 2
redistribute static subnets
network 192.168.20.0 0.0.0.255 area 0

ip route 8.8.8.8 255.255.255.255 192.168.20.2

RTRB#show run | se route
router ospf 2
redistribute static subnets
network 192.168.20.0 0.0.0.255 area 0
network 192.168.30.0 0.0.0.255 area 0
ip route 9.9.9.9 255.255.255.255 192.168.30.2

As seen 8.8.8.8 is missing from the process 1 (external route) on RTRA, only if I add redistribute static subnets to OSPF 1 this works:

RTRA#show ip ospf database

OSPF Router with ID (192.168.10.1) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
192.168.10.1 192.168.10.1 1054 0x80000006 0x001F3A 1
192.168.10.2 192.168.10.2 986 0x80000004 0x001B3F 1

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
192.168.10.2 192.168.10.2 986 0x80000002 0x00C49F

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag
9.9.9.9 192.168.10.1 309 0x80000002 0x00ED19 0

[Harold Ritter · Accepted solution]

Hi Chris,

This is the correct behavior. The static route is redistributed in process 2, but cannot be redistributed in process 1 via process 2, as it is not installed in the RIB as an ospf route. Using "redistribute static subnets" under ospf 1 is the right way to do it.

Regards,

[MHM Cisco World]

R-B have only one Process which is OSPF 1
R-A have only one process which is OSPF 2
R-C have two process which is OSPF 1 & 2 ?
Now your Q. is if the R-B have static route then it will forward to other process BUT same not happened in R-C??

[Giuseppe Larosa · Accepted solution]

Hello Chris,

Harold is right when using redistribution between routing protocols, including two different OSPF processes, only prefixes that are installed in the IP routing table are actually redistributed ( with just an exemption for connected subnets).

So in this case prefix 8.8.8.8./32 is  installed in IP routing table as S [1/0] via 192.168.20.2.

OSPF process 2 using redistribute static subnets is able to import the route and to create an LSA type 5  for 8.8.8.8

OSPF process 1 using redsitribute ospf 2 subnets cannot do the same as prefix 8.8.8.8 is present in OSPF process 2 database as an LSA type 5 but it is not installed in IP routing table.

When you add redistribute static subnets under router ospf 1 it is able to create an LSA type 5 from the static route.

This is correct behaviour and expected.

Hope to help

Giuseppe

[MHM Cisco World]

Hi Friend I know you mention that this issue solve BUT 
I don't get how? if we config static route then we don't benefit from redistribute, and we need static route for all route behind process 2.

So I think and try and config LAB and finally I get the solution. 
in order to not suboptimal redistribute from the two process I think Cisco Router give a feature that we 
CAN NOT REDISTRIBUTE FROM ONE PROCESS TO OTHER AND THEN RE-REDISTRIBUTE.

the solution is simply by 

redistribute ospf 1 subnet match internal. 

try my solution and I wait your reply.

[Harold Ritter]

Hi Mahmood,

The original question was more around, why static route 8.8.8.8/32 that has been redistributed in ospf 2 is not automatically redistributed into ospf 1, since there is a "redistribute ospf 2 subnets" under router ospf 1.

The answer is that 8.8.8.8/32 is not going to be redistributed from ospf 2 to ospf 1, even though it is in ospf 2 lsdb, because it is not installed in the local RIB as an ospf route, but rather as a static route.

The solution in this specific case is to use the "redistribute static subnets" under "router ospf 1" as well.

Regards,