RIP and OSPF Redistribution Environment

Consider Figure 12.2, which shows a redistribution scenario in which the routing protocols in use are RIP and OSPF. Routers B3 and B4 are running OSPF, router B1 is running RIP, and router B2 is running both routing protocols, RIP and OSPF, and is redistributing between the two.

Figure 12.2: Redistribution scenario running OSPF and RIP.

Table 12.2: Router Configuration

Router	Relevant Part of Configuration
B1	interface Serial1 ip address 192.168.10.1 255.255.255.252
	!
	interface Ethernet0
	ip address 10.10.1.1 255.255.255.0
	!
	router rip
	network 192.168.10.0
	network 10.10.1.0
	!
B2	interface Serial1
	ip address 192.168.10.2 255.255.255.252
	!
	interface Serial2
	ip address 192.168.1.1 255.255.255.252
	!
	interface Ethernet0
	ip address 172.16.128.1 255.255.255.128
	!
	router rip
	network 192.168.10.0
	network 172.16.128.0
	redistribute ospf 1 metric 1
	!
	router ospf 1
	network 192.168.1.0 0.0.0.255 area0
	redistrbute rip metric 1000
	!
B3	!
	interface Serial0
	ip address 192.168.1.2 255.255.255.252
	!
	interface Ethernet1
	ip address 172.16.12.1 255.255.255.0
	!
	interface Serial2
	ip address 192.168.2.1 255.255.255.252
	!
	router ospf 1
	network 192.168.1.0 0.0.0.255 area0
	network 192.168.2.0 0.0.0.255 area0
	network 172.16.12.0 0.0.0.255 area0
	!
B4	!
	interface Ethernet0
	ip address 10.10.12.1 255.255.255.224
	!
	interface Serial1
	ip address 192.168.2.2 255.255.255.252
	!
	router ospf 1
	network 192.168.2.0 0.0.0.255 area0
	network 10.10.12.0 0.0.0.255 area0
	!

In Figure 12.2:

• Network 10.10.12.0/27 is unreachable from the RIP domain.

• Network 172.16.12.0/24 is unreachable from the RIP domain.

Network 10.10.12.0/27 Unreachable from RIP Domain

To troubleshoot this problem:

1. Check if the corresponding interface in B4 is up by using the show ip interface brief command. The output of the command shows that the interface is up and running.

2. Check if routing is enabled for this network at B4 by using the show ip protocols command.

3. Check availability of route 10.10.12.0/27 in the OSPF routing domain by using the show ip route 10.10.12.0/27 command. The output of this command shows that the routing for network 10.10.12.0/27 is enabled and is propagated in the OSPF routing domain.

4. Check for the presence of route maps or filters in the redistribution configuration at B2 by using the show running-config command. The output of the command shows that there are no such restrictions on redistribution.

5. Check if there is any subnet of the major network 10.0.0.0/8 in the RIP domain. There could be a subnet mismatch, because this is a case of redistribution between a classful routing protocol, RIP, and a classless routing protocol, OSPF. Use the show ip route | inc 10 command to check this. The output of the command shows that there is a network 10.10.1.0/24 in the RIP domain and network 10.10.12.0/27, which is redistributed into RIP from OSPF, is not propagated in the RIP domain.

The modified configuration to ensure that network 10.10.12.0/27 is available in RIP domain is given by the command:

B2(config)#ip route 10.10.12.0 255.255.255.0 Null0 B2(config)#router rip B2(config-router)#redistribute static metric 1

Using this configuration, solve the current redistribution problem. RIP will propagate network 10.10.12.0/24 with a next-hop of B2, which has a more specific route to the subnet 10.10.12.0/27.

There can be issues if any other subnet of 10.10.12.0/24 is located outside the OSPF domain. In that case, there are two approaches to troubleshoot the problem. The IP addressing scheme can be modified to ensure that all subnets of 10.10.12.0/24 are located within the OSPF domain. Otherwise, static routes need to be defined for the other subnets that are not part of the OSPF domain. As a result, the /24 network will be pointed towards the OSPF domain, but there will be routers with longer netmasks available for a better match, pointed elsewhere, either within the RIP domain or if any other routing protocol environment is in use in the network.

Network 172.16.12. 0/24 Unreachable from RIP Domain

As discussed in the previous section, follow the steps to check and ascertain that route 172.16.12.0/24 is propagated within the OSPF domain but is not propagated within the RIP domain despite being redistributed. There could be a subnet mismatch. In that case:

1. Check if there is any subnet of the major network 172.16.0.0/16 in the RIP domain by using the show ip route | inc 172.16 command. The output of the command proves the presence of a network 172.16.128.0/25 in the RIP domain. The network 172.16.12.0/24 redistributed into RIP from OSPF is not propagated in the RIP domain.

2. Break down the OSPF network into subnets of the same netmask and redistribute into OSPF. The commands used for this are:

   B2(config)#ip route 172.16.12.0 255.255.255.128 Serial2 B2(config)#ip route 172.16.12.128 255.255.255.128 Serial2 B2(config)#router rip B2(config-router)#redistribute static metric 1

After this modification, the route for network 172.1.6.12.0/24 will be available in the RIP domain but as a part of two different subnets and not a single subnet.