IPv4 Redistribution - Lesson 01

A. Configure above mention network by using EIGRP AS 50 and OSPF Area 0 and make sure to advertise all networks on three routers. But do not implement any summarization on either EIGRP or OSPF. Then configure R3's loopback interfaces as a point to point OSPF network and try to understand about what happen to R2's routing table.

R1 Configuration

R1 (config) # router eigrp 50

R1 (config-router) # network 10.1.0.0 0.0.255.255

R1 (config-router) # no auto-summary

R2 Configuration

R2 (config) # router eigrp 50

R2 (config-router) # network 10.1.0.0 0.0.255.255

R2 (config-router) # no auto-summary

R2 (config-router) # exit

R2 (config) # router ospf 1

R2 (config-router) # network 10.1.40.0 0.0.0.255 area 0

R3 Configuration

R3 (config) # router ospf 1

R3 (config-router) # network 10.1.0.0 0.0.255.255 area 0

R3 (config-router) # network 10.1.1.4 0.0.0.0 area 0

Now in R2 # show ip route just shown /32. how to make it as /30 as the real network. Simple: configure all loopback interfaces as point to point

R3 Configuration

R3 (config) # int loopback 1

R3 (config-if) # ip ospf network point-to-point

Now in # show ip route at R2 will show /30 as the real network.

B. After configuring the basic set up, enable full redistribution between EIGRP and OSPF (use any method to ensure all three routers are able to see all routers) and make sure OSPF external routes should not increment their metric.

We can implement a necessary seed metric to ensure all three routers are able to see each and every routes. Then we focused on to OSPF external routes should not increment their metric value as they propagate through the network. 

What is seed metric? Each routing protocol has got its own seed metric which is assigned by default redistributed routes when no metric value in configured manually. Here are OSOF and EIGRP values for the protocol when no metric is defined with the metric argument on the redistribute command. (OSPF - 20 and EIGRP - infinite).

E1 type --> increment their metric value as they propagate the network

R2 Configuration

R2 (config) # router ospf 1

R2 (config-router) # redistribution eigrp 50 subnets (we use subnets option coz we have no permission to use summarization features in this problem)

R3 # show ip route

O E2    10.1.2.0/24 [110/20] via 10.1.40.2, 00:00:05, Serial0/0

O E2    10.1.1.0/24 [110/20] via 10.1.40.2, 00:00:05, Serial0/0

OSPF has default seed metric as 20. That's why EIGRP routes shown in the R3's routing table.

R2 (config-router) # redistribution eigrp 50 subnets metric 100

Then that 100 metric value goes into the routing table.

O E2    10.1.2.0/24 [110/100] via 10.1.40.2, 00:00:05, Serial0/0

R2 (config-router) # redistribution eigrp 50 subnets metric-type 2

In OSPF metric type get as E2 by default. but you can configure by using above command.

Now let's see redistribution of EIGRP! It looks different than OSPF.

R2 Configuration

R2 (config) # router eigrp 50

R2 (config-router) # redistribution ospf 1

--> R1 router still not showing he routing table with OSPF routes because EIGRP sends it's metric as infinity in redistribution. so we have to set it manually to some value which EIGRP has to be. 

R2 (config-router) # redistribution ospf 1 metric 100 100 100 100 100

(Bandwidth | delay | reliability | loading | MTU)

Now you can see OSPF routes in R1 routing table and you also can ping from R3 to R1.

D EX    10.1.1.4/30 [170/26137600] via 10.1.30.2, 00:00:08, Serial0/0

C. Make a distribute list filtering to get only 10.1.1.0 and 10.1.2.0 networks which are coming from the R1 router and 10.1.30.0 networks should be hidden from OSPF domain.

R2(config)#access-list 1 permit 10.1.1.0 0.0.0.255

R2(config)#access-list 1 permit 10.1.2.0 0.0.0.255

R2(config)#router ospf 1

R2(config-router)#distribute-list 1 out

R3# show ip route --> it will show only 10.1.1.0 and 10.1.2.0 networks and 10.1.30.0 is hidden.

D. make a route map to view only /24 subnet mask coming form OSPF domain.

At here we need prefix list feature to do this because access list command is little bit long to do so. Let's see how about the configuration. 

R2 (config) # ip prefix-list ITDIGEST permit 10.0.0.0/8 le 24

This command will permit for all subnet mask that less than 24. For instance consider about 10.0.2.6/24 network is coming from OSPF domain. Then R2 asked from that network 'do you part of 10' if it says yes. ok then let's look at for its prefix as less than or equal to 24. yes. Then permit it to allow

R2 (config) # route-map FILTER_O_TO_E

R2 (config-route-map) # match ip address prefix-list ITDIGEST

R2 (config-route-map) # exit

R2 (config) # router eigrp 50

R2 (config-router) # redistribution ospf 1 metric 100 100 100 100 100 route-map FILTER_O_TO_E

Now in R1 # show ip router will not show subnet mask which is greater that /24.

To save your configuration: copy run start

Thank you! If you have any doubts, please don't hesitate to ask form us.