redistribution of eigrp into ospf

In this example, Router B has two Fast Ethernet interfaces. FastEthernet 0/0 is in network 10.1.1.0/24 and FastEthernet 0/1 is in network 20.1.1.0/24. Router B is running EIGRP with Router A, and OSPF with Router C. Router B is mutually redistributing between the EIGRP and OSPF processes. This is the pertinent configuration information for Router B:

Router B

interface FastEthernet0/0
ip address 10.1.1.4 255.255.255.0

interface FastEthernet0/1
ip address 20.1.1.4 255.255.255.0

router eigrp 7
redistribute ospf 7 metric 10000 100 255 1 1500
network 10.1.1.0 0.0.0.255
auto-summary
no eigrp log-neighbor-changes
!
router ospf 7
log-adjacency-changes
redistribute eigrp 7 subnets
network 20.1.1.0 0.0.0.255 area 0
If you look at the routing table for Router B, you see the following:

routerB#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route

Gateway of last resort is not set

20.0.0.0/24 is subnetted, 1 subnets
C 20.1.1.0 is directly connected, FastEthernet0/1
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, FastEthernet0/0
From the configuration and the routing table above there are three things to notice:

The networks in question are in Router B routing table as directly connected networks.

Network 10.1.1.0/24 is part of the EIGRP process and network 20.1.1.0/24 is part of the OSPF process.

Router B is mutually redistributing between EIGRP and OSPF.

Below are the routing tables for Routers A and C.

routerA#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR

Gateway of last resort is not set

10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, FastEthernet0
20.0.0.0/24 is subnetted, 1 subnets
D EX 20.1.1.0 [170/284160] via 10.1.1.4, 00:07:26, FastEthernet0


routerC#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route

Gateway of last resort is not set

20.0.0.0/24 is subnetted, 1 subnets
C 20.1.1.0 is directly connected, FastEthernet1
O E2 10.1.1.0 [110/20] via 20.1.1.4, 00:07:32, FastEthernet1
Router A has learned about network 20.1.1.0/24 via EIGRP, which is shown as an external route, because it was redistributed from OSPF into EIGRP. Router C has learned about network 10.1.1.0/24 via OSPF as an external route, because it was redistributed from EIGRP into OSPF. Although Router B is not redistributing connected networks, it does advertise the network 10.1.1.0/24, which is part of the EIGRP process redistributed into OSPF. Similarly, Router B advertises network 20.1.1.0/24, which is part of the OSPF process redistributed into EIGRP.

Refer to Redistributing Connected Networks into OSPF for more information about connected routes being redistributed into OSPF.

Note: By default, only EBGP-learned information is candidate to be redistributed into IGP when the redistibute bgp command is issued. The IBGP routes is not redistributed into IGP until the bgp redistribute-internal command is configured under the router bgp command. But precautions must be taken in order to avoid loops within the Autonomous System when IBGP routes are redistirbuted into IGP.

Avoiding Problems Due to Redistribution