Refer to the exhibit. Router B is performing bidirectional redistribution between EIGRP and OSPF. The network 10.100.1.0/24 should not be reachable from the 10.100.9.0/24 network. However, it needs to be reachable from any network within the EIGRP domain. All other networks should be seen in both domains.
Which change to router B would accomplish these goals?
Select the best response.
A.
Under the EIGRP process, insert the distribute-list block_net_1 out ospf 1 command.
B.
Under the OSPF process, insert the distribute-list block_net_1 in serial1/0 command.
C.
Under the EIGRP process, insert the distribute-list block_net_1 in serial1/0 command.
D.
Under the OSPF process, insert the distribute-list block_net_1 out eigrp 1 command.
I am not sure about this answer.i guess that choice A is the correct one.Can anyone explain if not?
@Basem, I agree with you that A seems to be the best choice. With option D, ospf’s updates in the outbound direction into eigrp will be filtered by the access list. But the subnet we want to filter out (10.100.1.0/24) is not in the ospf domain but rather in the eigrp domain.
with option A, eigrp will filter 10.100.1.0/24 through the access list in the outbound direction to the ospf domain. Networks in the ospf domain will not have this route so the network 10.100.1.0/24 will not be reachable from the ospf domain, including from th 10.100.9.0/24 subnet.
I hope someone can shed some more light on this.
On second thought, I think option D is the right answer. My reason being that the command distribute-list block_net_1 out eigrp 1 under router ospf 1 will affect what updates (learnt from eigrp) OSPF sends into its routing domain. In this case, the access list will effectively filter out the 10.100.1/24 subnet from the updates sent to C within the ospf domain. C will thus not have an entry for the 10.100.1/24 prefix
Thanks your explanation.
I also think D is the right answer.
It is important to understand the differences between these commands:
•
The distribute-list out command filters updates going out of the interface or routing protocol
specified in the command, into the routing process under which it is configured.
•
The distribute-list in command filters updates going into the interface specified in the
command, into the routing process under which it is configured.
Answer: D
Explanation
The network 10.100.1.0/24 should not be reachable from network 10.100.9.0/24 -> we need to filter updates from EIGRP to OSPF so that the routing table of router C doesn’t have network 10.100.1.0/24 -> we need to filter it under OSPF process and the direction should be out of router B -> D is correct.