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Difficulty: MediumLayer 2 and Layer 3 EtherChannel (LACP)

A network administrator is configuring a routed (Layer 3) EtherChannel bundle using LACP on a Cisco Catalyst switch. The administrator creates the logical interface using `interface Port-channel 10`, executes `no switchport`, and assigns an IPv4 address. Next, the administrator enters interface configuration mode for GigabitEthernet0/1, GigabitEthernet0/2, and GigabitEthernet0/3. On GigabitEthernet0/1 and GigabitEthernet0/2, the administrator issues `no switchport` followed by `channel-group 10 mode active`. However, on interface GigabitEthernet0/3, the administrator issues `channel-group 10 mode active` without first executing `no switchport`.

What is the resulting operational status of interface GigabitEthernet0/3 in the output of `show etherchannel summary`?

  1. It remains in an independent (I) state and fails to bundle because its Layer 2 switchport mode does not match the Layer 3 configuration of the Port-Channel.Answer
  2. B
    It automatically converts to a routed port and bundles successfully into Port-Channel 10 upon receiving LACP negotiation frames from the neighbor switch.
  3. C
    It bundles into Port-Channel 10 successfully, but forces the entire EtherChannel bundle into a down state due to a native VLAN mismatch.
  4. D
    It automatically switches its negotiation mode from active to passive to reconcile the default Layer 2 switchport setting with the Port-Channel.

Answer

The interface remains in an independent (I) state and fails to join the EtherChannel bundle because its Layer 2 switchport setting does not match the Layer 3 configuration of the logical Port-Channel interface.
For a physical interface to join a Layer 3 EtherChannel, both the logical Port-Channel and all member physical interfaces must have 'no switchport' configured. Because GigabitEthernet0/3 retains its default Layer 2 switchport state, it fails the parameter compatibility check and is placed in an independent (I) state in 'show etherchannel summary'.

Step-by-Step Solution

1
Identify the configuration of the logical Port-Channel interface.
Port-channel 10 is configured as a Layer 3 (routed) interface via the 'no switchport' command.
EtherChannel member interfaces must match key operational attributes with the Port-Channel interface, including speed, duplex, trunking/routed mode, and allowed VLANs.
2
Analyze the configuration of physical interface GigabitEthernet0/3.
GigabitEthernet0/3 was added to channel-group 10 without executing 'no switchport'.
By default, switch ports operate as Layer 2 interfaces. Without 'no switchport', GigabitEthernet0/3 remains a Layer 2 port while Port-channel 10 is a Layer 3 port.
3
Determine the outcome in 'show etherchannel summary'.
GigabitEthernet0/3 is marked with the 'I' (Independent) flag and is excluded from the active bundle.
Cisco IOS enforces strict attribute consistency; incompatible physical ports are placed in an independent state and cannot aggregate into the channel.

Key Concept

Layer 3 EtherChannel Member Interface Compatibility Requirements
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Topics

Layer 2 and Layer 3 EtherChannel (LACP)

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