In the shown RIP topology, you do not want router R3 to receive any RIP routing updates. Which configuration change on R1 is typically used to prevent sending RIP updates out a specific interface toward R3 while still allowing RIP elsewhere?

Introduction / Context:
This question deals with controlling the behavior of distance-vector routing protocols, specifically RIP, on a per-interface basis. There are many situations where you want a router to participate in a routing protocol on some interfaces but not send updates out others, for example when connecting to an end host or a router that should not receive dynamic routes.

Given Data / Assumptions:
- RIP is the routing protocol in use across multiple routers (R1, R2, R3, etc.).
- Router R3 is connected to R1, but you do not want R3 to receive RIP updates from R1.
- You still want R1 to run RIP on its other interfaces and exchange routes with other routers in the topology.
- The question asks which configuration change should be made to achieve this behavior.

Concept / Approach:
In Cisco IOS, the passive-interface command within a routing protocol configuration tells the router not to send routing updates out that interface, while still listening for updates on other interfaces and advertising the connected network in the routing process. With RIP, making an interface passive effectively stops RIP broadcast or multicast updates from going out that interface. This is a clean way to prevent a neighbor from receiving updates without disabling RIP globally or changing protocols.

Step-by-Step Solution:
Step 1: Enter router configuration mode for RIP on R1 using router rip.Step 2: Identify the interface facing R3, for example serial0/0 or fastethernet0/1, depending on the topology.Step 3: Use the command passive-interface <interface-name> to stop RIP updates from being sent out that interface.Step 4: Confirm that R1 still participates in RIP on other interfaces and learns routes from the rest of the network.Step 5: Verify that R3 no longer receives RIP updates from R1 by checking its routing table or debug output.

Verification / Alternative check:
In a lab, before configuring passive-interface, you can run debug ip rip on R3 and see periodic incoming updates from R1. After configuring passive-interface on the relevant interface on R1, those updates will stop, while other routers still exchange RIP updates. R3's routing table will no longer be populated with routes learned from R1 by RIP, which confirms that the configuration change had the intended effect.

Why Other Options Are Wrong:
Option B incorrectly suggests that no configuration is needed, but RIP will send updates out all interfaces that match the network statements by default. Option C complicates the design by adding subinterfaces and VLANs without directly addressing RIP behavior. Option D replaces RIP with OSPF across the entire network, which is far more disruptive and outside the scope of the requirement. Option E disables routing on R3 itself, which may break other functions and is not necessary just to stop R3 from receiving RIP updates from R1.

Common Pitfalls:
Some administrators attempt to remove the network statement for the R3-facing network from R1's RIP configuration, but this can prevent R1 from advertising that connected network to others. Another pitfall is using distribute-lists when simply suppressing updates on a given interface would be simpler. Remember that passive-interface is the standard, exam-tested tool for suppressing routing protocol advertisements on a per-interface basis while keeping the protocol active elsewhere.

Final Answer:
You should configure a passive-interface on R1 for the interface that connects to R3 so that R1 does not send RIP updates out toward R3.