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Difficulty: MediumLayer 2 and Layer 3 EtherChannel (LACP)

A network administrator issue the `show etherchannel summary` command on a Cisco Catalyst switch to inspect an operational Link Aggregation Control Protocol (LACP) link bundle. The output displays the following status:

text
Flags: D - down P - bundled in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SD) LACP Gi0/1(I) Gi0/2(I)

Which configuration issue is the primary cause of the bundle remaining inactive with member ports in an independent state?

  1. Both the local and neighbor switches are configured in LACP passive negotiation mode on member interfaces.Answer
  2. B
    The local switch is configured in LACP active mode while the neighbor switch is configured in LACP passive mode.
  3. C
    The member interfaces have a native VLAN mismatch across the trunk link between the local and neighbor switches.
  4. D
    The local member interfaces are configured with 'channel-group 1 mode on' while the neighbor interfaces are configured in LACP active mode.

Answer

Both the local and neighbor switches are configured in LACP passive negotiation mode on member interfaces.
LACP requires at least one switch interface to be in 'active' mode to send LACP negotiation frames (PDUs). When both sides are set to 'passive' mode, neither switch initiates LACP messages. As a result, negotiation never occurs, physical interfaces remain in an independent/stand-alone (I) state, and the port-channel interface stays down (SD).

Step-by-Step Solution

1
Analyze the CLI output flags and port states.
Port-channel 1 has flags (SD), indicating it is Layer 2 and Down. Interfaces GigabitEthernet0/1 and 0/2 have flag (I), meaning they are operating as independent physical ports rather than bundled members.
LACP negotiation has failed to form a channel aggregator.
2
Evaluate LACP operational mode behaviors.
LACP 'active' mode sends LACP PDUs continuously. LACP 'passive' mode only responds to received LACP PDUs and never initiates negotiation.
If both connected switches are set to passive mode, neither switch sends initiating LACP frames, preventing negotiation entirely.
3
Determine the root cause of the independent (I) state.
Passive-to-passive LACP configuration leaves all physical interfaces in stand-alone (I) mode because zero LACP negotiation frames are exchanged.
At least one side must be set to 'active' mode for LACP negotiation to take place.

Key Concept

LACP Negotiation Modes (Active vs. Passive)
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Topics

Layer 2 and Layer 3 EtherChannel (LACP)

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