Which action fixes the issue while keeping the reachability from R5 to 10.1.1.0/24 network?

Refer to the exhibit.

To provide reachability to network 10.1.1.0/24 from R5, the network administrator redistributes EIGRP into OSPF on R3 but notices that R4 is now taking a suboptimal path through R5 to reach 10.1.1.0/24 network.

Which action fixes the issue while keeping the reachability from R5 to 10.1.1.0/24 network?
A . Change the administrative distance of OSPF to 200 on R5
B . Change the administrative distance of the external EIGRP to 90
C . Apply the outbound distribution list on R5 toward R4 in OSPF
D . Redistribute OSPF into EIGRP on R4

View Answer

Answer: B

Explanation

The subnet 10.1.1.1/24 is redistributed into EIGRP domain so it will have the Administrative Distance (AD) of 170. Therefore R4 also learns about this subnet advertised from R2 with the same AD of 170.

In the other hand, subnet 10.1.1.0/24 is also redistributed into OSPF on R3 so R5 & R4 will learn about this subnet with AD of 110, which is better than the above AD of 170 so R4 will choose path R4 -> R5 -> R3 -> R2 -> R1.

In order to solve this problem, we can configure an outbound distribute list on R5 to prevent (filter out) this subnet from advertising to R4. Then R4 only has one way to reach R1, which is R4 -> R2 – > R1. But this method will remove the backup route so it is not the best solution.

Another solution is to reduce the AD of the external EIGRP to a value smaller than 110. This method reserves the backup route in case of the main route fails -> This is the best solution.

To do this, we can use the following command on R4:

router eigrp 1

distance eigrp 90 91 //Changes the AD to 90 for internal EIGRP routes and changes the AD to 91 for EIGRP external routes

We tested this lab in GNS3 and you can read this lab here.

This is the result when we type the “distance eigrp …” command above on R4:

Note: We can change the AD of EIGRP routes via the “distance eigrp …” command but the effect of this command is local only.