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Difficulty: MediumLayer 2 and Layer 3 EtherChannel (LACP)

Two Cisco Catalyst switches are connected using four physical Ethernet links intended for a high-capacity trunk bundle. The interfaces on Switch-1 are configured with `channel-group 5 mode active`, while the interfaces on Switch-2 are configured with `channel-group 5 mode passive`. After connecting the cables, three of the four links bundle successfully into `Port-channel 5`, but interface `GigabitEthernet0/1` on Switch-1 remains in an Independent (`I`) operational state. What is the primary cause of this member interface failing to join the active LACP EtherChannel?

  1. The interface has an operational speed or duplex setting that does not match the other physical member interfaces in the bundle.Answer
  2. B
    Switch-2 is set to passive mode while Switch-1 is set to active mode, preventing full dynamic channel negotiation.
  3. C
    The native VLAN configured on GigabitEthernet0/1 differs from the trunk allowed VLAN list on the Port-channel interface.
  4. D
    The physical member interface requires PAgP desirable mode to negotiate with an LACP passive remote port.

Answer

The physical interface has an operational speed or duplex setting that does not match the other physical member interfaces in the bundle.
EtherChannel member interfaces must be configured identically regarding speed, duplex, media type, VLAN range, and trunking mode. If a single interface has a mismatched operational speed or duplex setting (e.g., auto-negotiated to 100/full instead of 1000/full), LACP consistency checks will fail for that port. Cisco IOS will flag the interface as Independent ('I') in the show etherchannel summary output, keeping it operating standalone outside the bundle while the matching ports form the EtherChannel.

Step-by-Step Solution

1
Analyze the LACP negotiation mode compatibility between Switch-1 and Switch-2.
Switch-1 is set to 'active' and Switch-2 is set to 'passive'. Active-to-passive is a valid LACP negotiation combination, so mode mismatch between switches is not the issue.
LACP active mode actively sends LACPDU packets, while passive mode responds to incoming LACPDUs.
2
Identify mandatory prerequisite physical interface matching parameters for EtherChannel member ports.
All member ports in an EtherChannel bundle must match speed, duplex, interface mode (access/trunk), native VLAN, and allowed VLANs.
If any individual physical port has a mismatched operational attribute (such as 100 Mbps when others are 1 Gbps), Cisco IOS prevents that port from joining the bundle to protect against frame misordering or forwarding loops.
3
Interpret the 'I' (Independent) flag in 'show etherchannel summary' output.
The 'I' flag indicates that the port is operating standalone (independently) because it failed EtherChannel consistency checks or negotiation.
Speed/duplex mismatch on that specific interface causes it to drop out of the logical bundle while remaining active as a standalone port.

Key Concept

EtherChannel Physical Interface Prerequisites & LACP Verification
Estimated Time:1m 15s
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Topics

Layer 2 and Layer 3 EtherChannel (LACP)

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