200-301 Question 338
Single answerA network engineer is configuring a point-to-point link between two routers using serial interfaces. After configuration, the engineer notices that the link is down, and the 'show ip interface brief' command indicates the interface status as 'serial0/0 is down, line protocol is down.' What could be the most likely cause of this issue?
- A
The encapsulation type on both ends of the link is mismatched.
- B
An incorrect IP address is configured on one of the router interfaces.
- C
The serial cable is not connected properly or is faulty.
- D
The bandwidth command is not configured on the interface.
Show answer and explanation
Correct answer: A
Explanation
In a point-to-point link, both ends of the connection must use the same encapsulation type (such as HDLC or PPP). A mismatch in encapsulation will result in the interface status showing 'down/down.' This is the most probable cause of the issue described in the scenario.
- A. Correct.
A mismatch in the encapsulation type (e.g., HDLC, PPP) between both ends of a point-to-point link will cause the link to fail, resulting in the 'down/down' status for the interface. This is the most likely issue in this scenario.
- B. Incorrect.
An incorrect IP address would not cause the interface to show 'down/down' status. Instead, it would prevent layer 3 connectivity but the interface would still be 'up/up' if the physical link is operational.
- C. Incorrect.
A faulty or improperly connected cable could cause the interface to show 'down/down,' but this is less likely as a cause compared to encapsulation mismatch in this scenario, especially since the question hints at configuration.
- D. Incorrect.
The bandwidth command does not impact the operational status of the interface. It is used for routing metrics and QoS calculations.