Cisco CCNA mock exam questions sample test – Question 370

.Your network is configured as shown in the following exhibit. When you trace traffic sourced from R3 destined for a LAN network off of R2 (not shown in the diagram), you see the
traffic is being forwarded from R1 to ISP1 rather than to R2.
Which of the following issues could NOT be causing this behavior?

A. The network command has not been executed on the interface leading to the LAN off R2
B. The passive interface command has been issued on the Gi0/4 interface of R1
C. A default route exists on R1 that leads to ISP1
D. RIPv2 has not been enabled on R2

Correct Answer: B

Explanation:
This issue would NOT be caused by executing the passive interface command on the Gi0/4 interface of R1. This command prevents the advertisement of RIP routes on that interface.
If that command had been issued, the traffic would not be forwarded to R1 because R3 would not know about the route to the LAN off of R2. This command would also prevent R3
from knowing about the default route to ISP1. Since the traffic is being routed to ISP1, this command must not have been executed.
All of the other options could potentially because traffic destined for R2 to be forwarded from R1 to ISP1, rather than to R2.
It is true that a default route exists on R1 that leads to ISP1. If this default route did not exist, the traffic destined for R2 would simply be dropped at R1 instead of being forwarded to
ISP1.
If the network command has not been executed on the interface leading to the LAN off of R2, the network leading to the LAN off R2 would not advertised by R2. That would make R1
unaware of this destination. In that case, R1 would use the default route to send traffic destined for R2 to ISP1. We know such a default route must exist, or the traffic would simply be
dropped at R1.
If RIPv2 has not been enabled on R2, R2 would not be receiving or advertising any RIP routes. When the packets destined for the network off of R2 arrive at R1, R1 will have not have
a route to that network. In that case R1 will forward the traffic to ISP1 using the default route.
Objective:
Routing Fundamentals
Sub-Objective:
Configure, verify, and troubleshoot RIPv2 for IPv4 (excluding authentication, filtering, manual summarization, redistribution)
References:
Cisco > Support > Technology Support > IP > IP Routing > Troubleshoot and Alerts > Troubleshooting TechNotes > How Does the Passive Interface Feature Work in EIGRP?
Networkers-Online > Routing > IGP > EIGRP > Passive-interface command behavior in RIP, EIGRP & OSPF