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Difficulty: MediumLayer 2 and Layer 3 EtherChannel (LACP)

An engineer is attempting to deploy a routed Layer 3 EtherChannel between two distribution switches. The logical interface `Port-channel 1` has been configured with `no switchport` and assigned an IPv4 address. However, executing `show etherchannel summary` reveals the following output:

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 f - failed to allocate aggregator

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

Which configuration step is required on the local switch to resolve this issue and bring the EtherChannel to an operational `SU` state?

  1. Execute the `no switchport` command on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 before bundling them into the channel group.Answer
  2. B
    Change the LACP mode on GigabitEthernet0/1 and GigabitEthernet0/2 from `passive` to `desirable` to force channel negotiation.
  3. C
    Configure matching native VLAN identifiers on GigabitEthernet0/1 and GigabitEthernet0/2 to match the Port-channel interface.
  4. D
    Change the LACP channel-group mode from `active` to `passive` on both member interfaces of the switch.

Answer

Execute the `no switchport` command on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2 before bundling them into the channel group.
In Cisco IOS/IOS-XE, creating a routed (Layer 3) EtherChannel requires disabling Layer 2 switching capabilities using `no switchport` on both the physical member interfaces (GigabitEthernet0/1 and GigabitEthernet0/2) and the logical Port-Channel interface. When physical ports remain configured as Layer 2 switchports while the port-channel is routed, the physical ports cannot be bundled, showing flag `I` (stand-alone), and the port-channel shows flag `S` (Layer 2) and `D` (Down).

Step-by-Step Solution

1
Analyze the `show etherchannel summary` flags
Po1 status is `SD` (Layer 2, Down) and member ports Gi0/1 and Gi0/2 are marked with flag `I` (Stand-alone).
The flag `S` indicates the port-channel is operating in Layer 2 mode instead of Layer 3 (`R`), causing a capability mismatch with the Layer 3 logical interface setup.
2
Identify missing physical interface commands
The physical member interfaces Gi0/1 and Gi0/2 still have default Layer 2 `switchport` operational characteristics.
For a routed Layer 3 EtherChannel, `no switchport` must be applied to all participating physical member interfaces as well as the logical Port-Channel interface.
3
Determine the corrective configuration change
Entering interface range configuration mode for Gi0/1 - 2 and issuing `no switchport` converts the physical member interfaces to Layer 3, allowing them to successfully bundle (`P`) under `Po1(RU)`.
Layer matching across physical member ports and logical channel interfaces is mandatory for successful LACP aggregation.

Key Concept

Layer 3 EtherChannel Physical and Logical Port Matching
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Topics

Layer 2 and Layer 3 EtherChannel (LACP)

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