You copy a configuration file from a network host to a Cisco router RAM. The configuration appears correct, but the router still does not pass traffic. What is one likely cause of this problem?

Introduction / Context:
This question explores a common troubleshooting scenario when applying a saved configuration to a Cisco router. Even when the configuration file looks correct, the router may still fail to pass user traffic. Often, the issue is related to interface status and the fact that certain attributes, such as the shutdown state, may not be overridden simply by copying a configuration file into RAM.

Given Data / Assumptions:

• A configuration file has been copied from a network host to the router RAM, for example using copy tftp running-config.
• A review of the configuration shows that IP addresses, routing, and basic settings appear to be correct.
• Despite this, the router does not forward traffic as expected.
• No mention is made of manually issuing the no shutdown command on interfaces.

Concept / Approach:
When interfaces on a Cisco router are created or when default configurations exist, they often start in an administratively down state. The shutdown command must be removed with the no shutdown command to enable the interface. Copying a configuration into RAM merges the file with the existing running configuration; it does not automatically remove existing shutdown commands unless the file explicitly includes no shutdown statements. Therefore, it is possible for all interfaces to remain disabled even though the copied configuration contains correct addressing and routing.

Step-by-Step Solution:
Step 1: You copy the configuration from a TFTP server or other network host into running-config on the router.Step 2: The router merges the new configuration with the current running configuration instead of completely replacing it.Step 3: Interfaces that were previously in shutdown state remain shut unless the new configuration explicitly includes no shutdown commands.Step 4: When you examine the configuration, you see correct IP addresses and routing but may overlook the shutdown lines on each interface.Step 5: As a result, traffic does not pass because the interfaces are still administratively down, even though the configuration file seems correct.

Verification / Alternative check:
You can verify this behaviour by running show ip interface brief or show interfaces. These commands show the line status and protocol status of each interface. If the interfaces are administratively down, you must go into interface configuration mode and issue no shutdown. After bringing interfaces up, the router should start forwarding traffic according to the configuration.

Why Other Options Are Wrong:
Option A could be true in some cases, but the problem described emphasizes that the configuration looks correct, which suggests that interface states are more likely the issue.Option B is incorrect because copying a configuration into flash does not change running behaviour, and the scenario states that it was copied to RAM.Option D is unlikely because IOS corruption would typically cause boot failures or serious errors, not just lack of traffic forwarding.Option E is wrong because the router does not automatically revert to startup-config after a manual copy to running-config.

Common Pitfalls:
A frequent mistake is assuming that copying a configuration always enables interfaces automatically. In practice, you must verify interface status and manually use no shutdown where needed. Many lab exercises fail for this simple reason, so always include interface status checks in your troubleshooting process.

Final Answer:
A likely cause is that The copy operation did not change the default shutdown state of the interfaces in the running configuration, so the interfaces remain administratively down.