200-301 Question 258
Single answerA network administrator is troubleshooting connectivity issues between two routers, R1 and R2, connected via a serial interface. The administrator has confirmed that the interfaces are configured with correct IP addresses, but the routers cannot ping each other. What is the most likely issue causing the connectivity failure?
- A
A missing clock rate configuration on the DCE side of the serial link
- B
A mismatched subnet mask between the two routers
- C
An incorrect static route configuration on one or both routers
- D
The serial interfaces on both routers are in an administratively down state
Show answer and explanation
Correct answer: A
Explanation
For serial connections, the DCE device must provide a clock signal to the DTE device for communication to occur. If the DCE side of the link is not configured with a clock rate, the link will not establish, and the routers will not be able to ping each other even if IP addresses are configured correctly. This is a common configuration oversight in serial WAN setups.
- A. Correct.
A missing clock rate configuration on the DCE side of the serial link will prevent the link from establishing a connection, as the clock rate is required for synchronization on serial WAN links.
- B. Incorrect.
A mismatched subnet mask could cause issues with routing, but it would typically not prevent the link from being established if the interfaces are correctly configured.
- C. Incorrect.
An incorrect static route configuration could cause issues with routing traffic between networks, but it would not prevent the routers from pinging each other on directly connected interfaces.
- D. Incorrect.
If the serial interfaces are administratively down, the administrator would have noticed this when checking the interface status, and it would be explicitly indicated as 'administratively down.'