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Difficulty: EasyLayer 2 and Layer 3 EtherChannel (LACP)

A network engineer is configuring a Link Aggregation Control Protocol (LACP) EtherChannel between two switches. Which TWO channel-group mode combinations between the interconnected switch ports will successfully establish an operational EtherChannel bundle? (Select two.)

  1. Active mode on the local switch port and active mode on the remote switch portAnswer
  2. Active mode on the local switch port and passive mode on the remote switch portAnswer
  3. C
    Passive mode on the local switch port and passive mode on the remote switch port
  4. D
    Active mode on the local switch port and desirable mode on the remote switch port

Answer

The configurations that successfully form an LACP EtherChannel bundle are active-to-active and active-to-passive mode combinations.
For an IEEE 802.3ad Link Aggregation Control Protocol (LACP) EtherChannel to form, at least one interface must be set to active mode so that LACP frames are transmitted across the link. Consequently, combining an active interface with another active interface, or an active interface with a passive interface, results in a operational EtherChannel bundle.

Step-by-Step Solution

1
Analyze LACP mode behaviors
Active mode actively originates LACP negotiation frames. Passive mode only listens and responds to incoming LACP frames.
For negotiation to take place, at least one endpoint must generate negotiation frames.
2
Evaluate the mode combinations for compatibility
Active-to-active and active-to-passive form valid LACP EtherChannels. Passive-to-passive fails because neither interface transmits LACP negotiation frames. Active-to-desirable fails because LACP and PAgP are incompatible protocols.
EtherChannel negotiation protocols must match on both ends, and at least one port must actively send negotiation frames.

Key Concept

LACP EtherChannel Mode Negotiation Rules
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Topics

Layer 2 and Layer 3 EtherChannel (LACP)

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