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Difficulty: MediumLayer 2 and Layer 3 EtherChannel (LACP)

A network administrator is deploying a dynamic Layer 2 EtherChannel using the Link Aggregation Control Protocol (LACP) between Switch-A and Switch-B across two physical interfaces. Switch-A must actively initiate channel negotiation, whereas Switch-B must only listen and respond to incoming LACP negotiation requests.

Which two configuration statements correctly describe the settings required to establish this EtherChannel bundle? (Select two.)

  1. Switch-A member interfaces must be configured with channel-group 1 mode active.Answer
  2. B
    Switch-B member interfaces must be configured with channel-group 1 mode desirable.
  3. Switch-B member interfaces must be configured with channel-group 1 mode passive.Answer
  4. D
    Switch-A member interfaces can have differing native VLAN settings if Switch-B uses matching native VLANs on its local links.

Answer

To form an LACP EtherChannel where one switch actively initiates negotiation and the other responds, Switch-A member interfaces must be configured with 'channel-group 1 mode active' and Switch-B member interfaces must be configured with 'channel-group 1 mode passive'.
In LACP dynamic EtherChannel configuration, 'active' mode initiates LACP negotiations by sending LACP frames, while 'passive' mode responds to incoming LACP negotiation frames without sending them unprompted. An active-to-passive pairing successfully establishes the EtherChannel bundle.

Step-by-Step Solution

1
Analyze protocol negotiation requirements for LACP.
LACP supports two modes: active (initiates negotiation) and passive (responds to negotiation).
Switch-A must initiate negotiation, so it requires active mode. Switch-B must only respond, so it requires passive mode.
2
Evaluate protocol compatibility.
PAgP modes (desirable, auto) cannot pair with LACP modes (active, passive).
Configuring desirable mode on Switch-B attempts PAgP negotiation, causing negotiation failure with an LACP active switch.
3
Verify physical interface parameter consistency requirements.
All interfaces bundled into an EtherChannel on a local switch must share identical settings.
Mismatched native VLANs or trunk settings across member links on the same switch prevent the EtherChannel from bundling successfully.

Key Concept

LACP EtherChannel Mode Compatibility and Member Port Prerequisites
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Topics

Layer 2 and Layer 3 EtherChannel (LACP)

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