200-301 Question 337
Select 3A network engineer is configuring a point-to-point connection between two routers using a serial link. After the configuration, the link does not come up, and the engineer suspects an issue with the Layer 2 protocol. Which of the following steps should the engineer take to troubleshoot and resolve the issue?
- A
Verify that both ends of the link are using the same encapsulation protocol.
- B
Check for mismatched IP addresses on both ends of the link.
- C
Ensure that the clock rate is configured on the DCE side of the link.
- D
Verify that both routers are using dynamic routing protocols.
- E
Check the physical layer for issues such as loose cables or faulty hardware.
Show answer and explanation
Correct answers: A, C, E
Explanation
For a point-to-point serial link, proper Layer 2 configuration is critical. The encapsulation protocol must match on both ends of the link for communication to occur, and the DCE side must provide a clock rate for synchronization. Additionally, the physical layer should be checked for any hardware or cabling issues. These steps ensure a functioning point-to-point connection at the Layer 2 level.
- A. Correct.
Correct. Mismatched encapsulation protocols (e.g., PPP vs HDLC) can prevent the link from coming up as they define how frames are formatted and transmitted over the link.
- B. Incorrect.
Incorrect. IP addressing issues occur at Layer 3, but the problem described is related to the Layer 2 protocol. IP mismatches do not prevent the Layer 2 link from coming up.
- C. Correct.
Correct. Serial links require the clock rate to be set on the DCE (Data Communications Equipment) side for proper synchronization. Without this, the link cannot function.
- D. Incorrect.
Incorrect. While dynamic routing protocols are important for exchanging routing information, they are not relevant to the Layer 2 connectivity issue described in the scenario.
- E. Correct.
Correct. Physical layer issues such as loose cables or hardware faults can prevent the link from coming up, even if the Layer 2 configuration is correct.