OSPF Redistribution Problem

Projects-7 OSPF redistribution

Problem :-    Router R1 is advertising all of its network(s) in OSPF area 0. Router R2 is advertising E0/0 IP network 10.1.1.0/30 in OSPF area 0, E1/0 network 15.1.1.4/30 in EIGRP AS 100. R3 is advertising all three networks in EIGRP 100.

Redistribution is done from EIGRP AS 100 to OSPF Process Id 10 ( area 0) and vice versa.

Redistribution commands used as below

redistribute eigrp 100 metric 555                                ( Configured under  router ospf 10 )

redistribute ospf 10 metric 10000 100 255 1 1500   ( Configured under router eigrp 100)

From R1 I am not able to ping 100.1.1.19 but I am able to ping 140.1.1.19 . Why? What is wrong in redistribution.

Solution :-  when we redistribute networks in OSPF then we need to use a keyword “subnets” at the end of the command. So configuration should have been as below

redistribute eigrp 100 metric 555 subnets                                ( Configured under  router ospf 10 )

If we don’t use the keyword “subnets” then redistribution will only happen for classful networks. That’s the reason that ping is working for 140.1.1.19 because it has subnet mask of 255.255.0.0 i.e. /16 and 140 also belongs to Class B Range. Therefore, it is classful.

While 100.1.1.19/29 is part of 100.1.1.16/29 network and it is a classless i.e. network which is divided or subnetted.

Moreover, if we miss the keyword “subnets” while in redistribution then below message will generate

R2(config-router)#router os 10

R2(config-router)#redistribute eigrp 100 metric 555

% Only classful networks will be redistributed

R2(config-router)#

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