easyMultiple Choice
350-401 Practice Question: Is configuring an EtherChannel between two Cisco…
A network engineer is configuring an EtherChannel between two Cisco switches. The engineer wants to use PAgP and ensure that the channel forms only if the neighboring switch is also configured for PAgP. Which mode should be configured on the local switch?
⚠ Common exam trap
Cisco often tests the distinction between PAgP and LACP modes, and the trap here is that candidates confuse 'active' (LACP) with 'desirable' (PAgP), or assume 'auto' is sufficient when the requirement is to actively ensure the neighbor is also running PAgP.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure 'channel-group 1 mode desirable' on the physical ports.
PAgP (Port Aggregation Protocol) is a Cisco proprietary protocol that negotiates EtherChannel links. The 'desirable' mode actively sends PAgP packets to initiate negotiation and will form a channel only with a neighbor also running PAgP (either in 'desirable' or 'auto' mode). This meets the requirement of ensuring the channel forms only if the neighbor is configured for PAgP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure 'channel-group 1 mode desirable' on the physical ports.
Why this is correct
PAgP desirable mode actively transmits PAgP packets on the physical ports, initiating the negotiation to form an EtherChannel with the neighboring switch. This is the required behavior when the peer is configured with a PAgP mode such as desirable or auto, because desirable ensures that at least one side is driving the negotiation. It also validates that the ports on both ends meet consistency requirements before the channel is established.
- ✗
Configure 'channel-group 1 mode auto' on the physical ports.
Why it's wrong here
PAgP auto mode is purely passive: it listens for PAgP packets but never sends them, so it can form an EtherChannel only if the neighbor actively sends desirable packets. If both switches are set to auto, neither side transmits PAgP frames and the EtherChannel will not come up. Because the needed configuration must actively negotiate the bundle, auto is too passive and leaves the physical ports operating as independent links.
- ✗
Configure 'channel-group 1 mode active' on the physical ports.
Why it's wrong here
The 'active' keyword is an LACP (IEEE 802.3ad) mode, not a PAgP mode, so it is incompatible with a PAgP-based EtherChannel. If one switch runs LACP active while the other runs PAgP desirable, the two sides speak different control protocols and will never reach an agreement to bundle the ports. To use PAgP with active initiation, the correct keyword is 'desirable'.
- ✗
Configure 'channel-group 1 mode on' on the physical ports.
Why it's wrong here
The 'on' mode creates a static EtherChannel without running any negotiation protocol, meaning it does not send PAgP or LACP frames and does not verify the neighbor's configuration. While two manually configured 'on' ports may form a channel if both sides are forced, this does not satisfy a requirement to use PAgP negotiation. Additionally, static mode can hide mismatches in speed, duplex, or VLAN assignment, leading to forwarding problems or loops.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.