RIP + Split Horizon — Which Route Will NOT Be Advertised Back to the Neighbor? Given the routing table excerpt below (learned via RIP on Serial0 from neighbor 192.168.40.1), which single network will NOT be advertised back to that same neighbor due to the split horizon rule? R 192.168.30.0/24 [120/1] via 192.168.40.1, 00:00:12, Serial0 C 192.168.40.0/24 is directly connected, Serial0 C 172.16.30.0/24 is directly connected, Loopback0 C 192.168.50.0/24 is directly connected, Ethernet0

Introduction / Context:
Distance-vector protocols periodically advertise routes out interfaces. Split horizon says a router must not advertise a route back out the same interface on which it was learned. This prevents simple routing loops.

Given Data / Assumptions:

• Routes marked R were learned via RIP from 192.168.40.1 on Serial0.
• Connected networks (C) are locally known and are valid to advertise to neighbors.
• We are considering advertisements sent back to the same neighbor on Serial0.

Concept / Approach:
Under split horizon, any prefix learned from a neighbor on an interface is not advertised back out that interface to that neighbor. Locally connected networks (not learned via that neighbor) are eligible to be advertised. Therefore, of the listed options, only the RIP-learned route 192.168.30.0/24 will be suppressed when sending updates back to 192.168.40.1 over Serial0.

Step-by-Step Solution:
Identify learned-via-Serial0: 192.168.30.0/24 (R via 192.168.40.1).Identify locally connected: 172.16.30.0/24 (Loopback0), 192.168.50.0/24 (Ethernet0), and the link network 192.168.40.0/24.Apply split horizon: suppress only those learned on Serial0 when advertising out Serial0.Conclude the suppressed route is 192.168.30.0/24.

Verification / Alternative check:
Use debugging (debug ip rip) and observe that locally connected networks are advertised out Serial0, while the route learned from 192.168.40.1 (192.168.30.0/24) is omitted or poisoned depending on configuration.

Why Other Options Are Wrong:

• 172.16.30.0/24 and 192.168.50.0/24 are connected and will be advertised.
• 192.168.40.0/24 is the transit link itself; its advertisement behavior depends on implementation, but it is not a route learned from the neighbor in question.
• Claiming “None” ignores split horizon behavior.

Common Pitfalls:
Assuming all routes are suppressed; only routes learned on that same interface are suppressed, not connected routes or routes learned elsewhere.

Final Answer:
192.168.30.0/24