While troubleshooting an unreachable network, you suspect that a router along the path is failing. Which IOS user EXEC command helps you trace the route taken by packets to the remote network?

Introduction / Context:
When a destination network is unreachable, it is important to know at which hop along the path the traffic fails. Cisco IOS provides several user EXEC commands for basic troubleshooting. Understanding which command shows the path that packets take through multiple routers is essential for isolating faults in routed networks.

Given Data / Assumptions:

• The destination network cannot be reached from your current device.
• You suspect that some router along the path is malfunctioning or misconfigured.
• You are operating in user EXEC mode, indicated by the Router> prompt.
• You want to use a command that reveals each hop visited by packets on the way to the remote network.

Concept / Approach:
The traceroute utility (often abbreviated as trace on some IOS versions) sends probe packets with gradually increasing Time To Live values. Each router that forwards the packet decrements the TTL and may return an ICMP Time Exceeded message when the TTL reaches zero. By collecting these responses, traceroute builds a list of routers along the path. In Cisco IOS, the user EXEC command trace or traceroute is used to initiate this process. By contrast, ping tests reachability but does not show intermediate hops.

Step-by-Step Solution:
Step 1: From the Router> prompt, issue the command trace followed by the IP address of the unreachable network or host.Step 2: IOS begins sending packets with TTL values starting at one and collects responses from each router that returns ICMP Time Exceeded messages.Step 3: The device displays a list of hops, including the IP addresses of routers along the path, up to the point where the packets are dropped or the destination is reached.Step 4: Identify the last router in the list that responds. The next hop that does not respond is often where the problem lies.Step 5: Use this information to focus further troubleshooting efforts on that suspect router or link.

Verification / Alternative check:
You can compare traceroute results from different points in the network to see whether the same path is used and where packets are being lost. Combining traceroute results with ping tests and show ip route outputs gives a more complete picture of the routing problem, but only traceroute reveals each hop.

Why Other Options Are Wrong:
Option A (ping) verifies reachability and round trip time but does not show intermediate routers along the path.Option C (show ip route) displays the local routing table but does not show remote routers or where packets are being dropped.Option D (show interface) shows statistics and status for local interfaces only and does not reveal the path to a remote network.Option E (show cdp neighbors) lists directly connected Cisco devices, not the full routed path across the network.

Common Pitfalls:
Many administrators rely solely on ping when troubleshooting connectivity issues. While ping is useful, it cannot identify which specific hop is failing. Traceroute or trace is much better for isolating faults in complex routed environments where traffic may traverse many routers.

Final Answer:
The appropriate user EXEC command is Router> trace, which runs a traceroute to show the routers along the path to the unreachable network.