Redistribution Between RIP and OSPF

Objectives

• Review configuration and verification of RIP and OSPF.
• Configure passive interfaces in both RIP and OSPF.
• Filter routing updates using distribute lists.
• Redistribute static routes into RIP.
• Redistribute RIP routes into OSPF.
• Redistribute OSPF routes into RIP.
• Originate a default route into OSPF.
• Set a default seed metric.
• Modify OSPF external network types.
• Configure summary addresses.

Step 1: Configure loopbacks and assign addresses.

 

Step 2: Configure RIPv2.

Configuring RIPv2 on a router is fairly simple:
• Type the global configuration command router rip to enter RIP configuration mode.
• Enable RIPv2 with the version 2 command.
• Enter the no auto-summary command to disable automatic summarization at classful network boundaries.
• Add the networks you want using the network network command.

Q : Based on the topology diagram, which major networks need to be advertised into RIP for R1?

Ans : 

 

172.16.0.0/16
192.168.48.0/24
192.168.49.0/24
192.168.50.0/24
192.168.51.0/24
192.168.70.0/24

Q : Which major networks need to be advertised into RIP for R2?

Ans : Only 172.16.0.0/16

Step 3: Configure passive interfaces in RIP.

Q : What are some reasons to prevent RIP from sending updates out a particular interface?

Ans : RIPv2 does not use an adjacency system. Therefore, RIPv2 floods all of its routing updates out of its interfaces rather than developing adjacencies with short hello packets like EIGRP and OSPF. Because RIPv2 could flood packets out interfaces where there are no RIPv2 receivers, it is a best practice to prevent RIP packets from being sent out these interfaces.

 Q : Does RIPv2 send advertisements out loopback interfaces?

 Ans : By default, loopback interfaces act like normal interfaces in RIPv2 when sending and receiving packets. However, a router will never have RIPv2 neighbors out its loopback interface, so loopback interfaces can always be configured as passive interfaces, thereby saving CPU resources.

 

Step 4: Summarize a supernet with RIP. 

Q : Which RIP routes should you summarize because they are contiguous and which mask should you use?

Ans : Summarize 192.168.48.0/24 through 192.168.51.0/24. Use a 22-bit mask to create the supernet.

 

Q : Will this route to Null0 affect routing to prefixes with longer addresses on R1? Explain.

Ans : The routing table first matches based on longest IP prefix. If any of the summarized networks are routable on R1, as in this situation, R1 uses the connected route with the longer mask to reach those networks. If one of those interfaces were to be shut down, R1 would send traffic for that network to its Null0 virtual interface.

Step 5: Suppress routes using prefix lists.

Q : Why would you want to filter updates being sent out or coming in?

Ans : The intention is to summarize addresses at R1, achieving benefits such as smaller routing tables and the prevention of route flapping disturbing network stability. By redistributing the static route into RIPv2, only the summary route was added, but the more specific routes were not filtered. To achieve these benefits, filter the outgoing routes to R2 by allowing all routes except the 24-bit routes.

Step 6: Configure OSPF.

Q : You can verify this by viewing the output of the show ip route command on R2. Do you see a 192.168.0.0/16 supernet?

Ans :   No, because the network command selects interfaces by IP address. It does not set the exact prefix to be advertised.

 

Step 7: Configure passive interfaces in OSPF.

Q : How is this different from the RIP version of this command?

Ans : Passive interfaces in RIPv2 prevent outgoing routing information via multicast.
Because OSPF must create an adjacency before sending routing updates, the OSPF version of the passive-interface command prevents sending or processing OSPF packets and, therefore, prevents adjacencies.

Step 8: Allow one-way redistribution.

Step 9: Redistribute between two routing protocols.

Step 10: Set a default seed metric.

Step 11: Change the OSPF external network type.

Q : Where would an external type 1 metric be useful?

Ans : If there are multiple paths through an OSPF domain to an external destination network, use E1 routes so that OSPF will evaluate the shortest cost path. Especially use this option if multiple ASBRs are advertising the same destination network to prevent suboptimal routing.

Q : Where would an external type 2 metric be useful?

Ans : If there is only one ASBR advertising an external route, use E2 routes. In this scenario, use the E1 type even though only one ASBR is advertising the external routes.

Q : Which attributes of the routes changed?

Ans : The external route type has been changed from E2 to E1. The metric, previously 10000, has been incremented to represent the path through the OSPF network to the ASBR.

__________________________________________________________________________________

 Final Device Configuration :

R1#sh running-config
Building configuration...

Current configuration : 1821 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R1
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip subnet-zero
no ip icmp rate-limit unreachable
ip cef
ip tcp synwait-time 5
!        
no ip domain lookup
!
interface Loopback0
 ip address 172.16.1.1 255.255.255.0
!
interface Loopback48
 ip address 192.168.48.1 255.255.255.0
!
interface Loopback49
 ip address 192.168.49.1 255.255.255.0
!
interface Loopback50
 ip address 192.168.50.1 255.255.255.0
!
interface Loopback51
 ip address 192.168.51.1 255.255.255.0
!
interface Loopback70
 ip address 192.168.70.1 255.255.255.0
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/0
 ip address 172.16.12.1 255.255.255.0
 clock rate 64000
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/1
 no ip address
 shutdown
 clock rate 2000000
!
router rip
 version 2
 redistribute static
 passive-interface default
 no passive-interface Serial0/0
 network 172.16.0.0
 network 192.168.48.0
 network 192.168.49.0
 network 192.168.50.0
 network 192.168.51.0
 network 192.168.70.0
 distribute-list prefix RIP-OUT out Serial0/0
 no auto-summary
!
ip classless
ip route 192.168.48.0 255.255.252.0 Null0
!
no ip http server
no ip http secure-server
!
ip prefix-list RIP-OUT seq 5 permit 192.168.48.0/22
ip prefix-list RIP-OUT seq 10 deny 192.168.48.0/22 le 24
ip prefix-list RIP-OUT seq 15 permit 0.0.0.0/0 le 32
!
control-plane
!
line con 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line aux 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line vty 0 4
 login
!
!
end

____________________________________________________________________________

R2#show rUNning-config
Building configuration...

Current configuration : 1325 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R2
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip subnet-zero
no ip icmp rate-limit unreachable
ip cef
ip tcp synwait-time 5
!        
no ip domain lookup
!
interface Loopback0
 ip address 172.16.2.1 255.255.255.0
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/0
 bandwidth 64
 ip address 172.16.12.2 255.255.255.0
 clock rate 2000000
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/1
 ip address 172.16.23.2 255.255.255.0
 clock rate 64000
!
router ospf 1
 log-adjacency-changes
 redistribute rip metric-type 1 subnets
 network 172.16.23.0 0.0.0.255 area 0
 default-information originate
 default-metric 10000
!
router rip
 version 2
 redistribute ospf 1 metric 4
 passive-interface Loopback0
 network 172.16.0.0
 no auto-summary
!
ip classless
!
no ip http server
no ip http secure-server
!
control-plane
!
line con 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line aux 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line vty 0 4
 login
!        
!
end

______________________________________________________________________

R3#sh running-config
Building configuration...

Current configuration : 1725 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R3
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip subnet-zero
no ip icmp rate-limit unreachable
ip cef
ip tcp synwait-time 5
!        
no ip domain lookup
!
interface Loopback0
 ip address 172.16.3.1 255.255.255.0
 ip ospf network point-to-point
!
interface Loopback20
 ip address 192.168.20.1 255.255.255.0
 ip ospf network point-to-point
!
interface Loopback25
 ip address 192.168.25.1 255.255.255.0
 ip ospf network point-to-point
!
interface Loopback30
 ip address 192.168.30.1 255.255.255.0
 ip ospf network point-to-point
!
interface Loopback35
 ip address 192.168.35.1 255.255.255.0
 ip ospf network point-to-point
!
interface Loopback40
 ip address 192.168.40.1 255.255.255.0
 ip ospf network point-to-point
!
interface FastEthernet0/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/0
 bandwidth 64
 ip address 172.16.23.3 255.255.255.0
 clock rate 2000000
!
interface FastEthernet0/1
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial0/1
 no ip address
 shutdown
 clock rate 2000000
!
router ospf 1
 log-adjacency-changes
 passive-interface default
 no passive-interface Serial0/0
 network 172.16.0.0 0.0.255.255 area 0
 network 192.168.0.0 0.0.255.255 area 0
 default-metric 10000
!
ip classless
!
no ip http server
no ip http secure-server
!
control-plane
!
line con 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line aux 0
 exec-timeout 0 0
 privilege level 15
 logging synchronous
line vty 0 4
 login
!
!
end

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