350-401 Question 129
Single answerA network engineer has configured an EtherChannel between two Cisco switches using LACP. After completing the configuration, traffic is not flowing through the EtherChannel, and the link is down. Upon reviewing the configuration, the engineer notices that one side is set to 'active' mode while the other side is set to 'on' mode. What is the most likely reason for the issue?
- A
The 'on' mode does not negotiate protocols and is incompatible with LACP.
- B
The 'active' mode requires the other side to be configured as 'passive' for LACP to form successfully.
- C
The EtherChannel is configured with mismatched VLANs on the member interfaces.
- D
LACP requires both sides to use the same system priority for successful negotiation.
Show answer and explanation
Correct answer: A
Explanation
In this scenario, the issue arises because 'on' mode does not negotiate any protocols and is incompatible with LACP, which relies on negotiation. For LACP to work, both sides must use either 'active' or 'passive' mode (or a combination of both). Configuring one side to 'on' mode and the other to 'active' mode prevents the EtherChannel from forming, as 'on' mode does not participate in LACP protocol negotiations.
- A. Correct.
The 'on' mode forces an EtherChannel without protocol negotiation, making it incompatible with LACP modes ('active' or 'passive'). This is the most likely cause of the issue in this scenario.
- B. Incorrect.
While 'active' mode does require the other side to participate ('active' or 'passive'), the issue here is the 'on' mode, which does not use LACP at all.
- C. Incorrect.
Mismatched VLANs on member interfaces can cause issues with an EtherChannel, but this is not relevant to the described configuration issue involving LACP and 'on' mode.
- D. Incorrect.
LACP does not require both sides to have the same system priority for negotiation. System priority is used to determine which switch's LACP settings take precedence, but it does not prevent the EtherChannel from forming.