350-401 Question #17: Real Exam Question with Answer & Explanation

Question

To increase total throughput and redundancy on the links between the wireless controller and switch, the customer enabled LAG on the wireless controller. Which EtherChannel mode must be configured on the switch to allow the WLC to connect?

Options

• AAuto
• BActive
• COn
• DPassive

Explanation

LAG/EtherChannel Mode Explanation

Option C (On) is correct because Wireless LAN Controllers (WLCs) use a static LAG implementation that does not support dynamic negotiation protocols like LACP or PAgP. When the WLC has LAG enabled, the switch port must be configured in "On" mode, which forces the EtherChannel to be active unconditionally without waiting for any negotiation.

Why the distractors are wrong:

• Auto (A) is a PAgP passive mode that waits for the other side to initiate negotiation - since the WLC doesn't speak PAgP, no channel forms
• Active (B) is an LACP mode that sends negotiation frames - the WLC's static LAG cannot respond to LACP, so the channel won't establish
• Passive (D) is also an LACP mode that waits for LACP initiation - same problem as Active; no LACP response from the WLC means no channel

💡 Memory Tip: Think of it this way - WLCs are "stubborn" and only do things their way (static). To match a stubborn device, you must force the switch with "On" mode. If either side tries to negotiate, the WLC simply won't respond, and the link fails.

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