Question: Overlapping Connected and Routing Protocol Routes

certskills
By certskills April 22, 2014 09:05

This latest #CCNA question takes us in the same direction as the previous question: how does a router choose between different competing routes? Today’s question adds connected routes to the mix, along with routes learn by routing protocols.  Enjoy!

Previous similar question

Other Q&A in this blog

Background

Note: The background in this section is identical to the previous question in this blog.

For this question, router R1 runs RIP-2, and OSPF, and EIGRP. Admittedly, that’s a bit unusual for both the ICND1 and ICND2 exams, but to discuss how routers choose routes when learning those routes from multiple sources, at least one router has to run multiple routing protocols. The figure shows the subnet IDs/masks on the right, the routing protocols, and metrics.

If you look at the subnets on the right, its pretty obvious that the subnetting design is busted. Routers R2, R3, and R4 all connect to a subnet with subnet ID 10.1.2.0. Note however that each uses a different subnet mask. That, in a word, is bad.

More Background

Here’s the additional detail compared to the previous question…

In this case, R1 has also been configured with the ip address 10.1.2.0 255.255.255.0 command on its LAN interface.

The Question

Now to the question to ponder. Assuming all the links in the diagram work, and R1 indeed learns the routes using RIP-2, OSPF, and EIGRP. R1 also knows a connected route on its LAN interface as well. What does R1 put in its routing table? In other words, what will the output of R1’s show ip route command look like? (Select a single answer.)

A. It will list route 10.1.2.0/25, but not for 10.1.2.0/24, 10.1.2.0/26, nor 10.1.2.0/27

B. It will list route 10.1.2.0/26, but not for 10.1.2.0/24, 10.1.2.0/25, nor 10.1.2.0/27

C. It will list route 10.1.2.0/27, but not for 10.1.2.0/24, 10.1.2.0/25, nor 10.1.2.0/26

D. It will list route 10.1.2.0/24, but not for 10.1.2.0/25, 10.1.2.0/26, nor 10.1.2.0/27

E. It will list a route for both 10.1.2.0/24 and 10.1.2.0/27, but not the other two subnets

F. It will list a route for 10.1.2.0/24, 10.1.2.0/25, 10.1.2.0/26, and 10.1.2.0/27

 

Answer: Overlapping Connected and Routing Protocol Routes
Answer: Router Adding Routes when VLSM Subnets Overlap
certskills
By certskills April 22, 2014 09:05
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