LACP EtherChannel

LACP EtherChannel is an open-standard protocol defined by IEEE 802.3ad. It allows switches from different vendors to automatically bundle multiple physical links into a single logical connection.

Unlike Static EtherChannel, which relies on manual configuration on both sides, LACP automatically negotiates which interfaces can form the bundle.

How LACP Works

Each interface participating in an LACP EtherChannel operates in one of two modes:

• Active mode → the switch initiates the negotiation process.

• Passive mode → the switch waits for an LACP request before joining the bundle.

Figure 1 – LACP EtherChannel Using Passive and Active Modes

When one switch runs in Active mode and the other in Passive mode, the EtherChannel forms successfully.
If both sides are Passive, no negotiation starts, and the aggregation does not form.

For example, if SW1 uses Passive mode and SW2 uses Active mode, they automatically create a Port-Channel, grouping several physical interfaces into one logical link.

Before You Begin

Before configuring LACP EtherChannel,make sure all participating interfaces meet the following conditions:

• Interface consistency: all interfaces must operate with the same speed, duplex, and type.

• Trunking or VLAN alignment: for Layer 2 operation, interfaces must share identical VLAN or trunk configurations.

• Operational status: each physical link must be active.

Figure 2 – LACP Link Requirements

If any of these conditions are not met, the EtherChannel will fail to form even with LACP enabled.
Once your interfaces are verified and consistent, you can move on to the configuration phase.

For this configuration, we will use GigabitEthernet interfaces running in full-duplex mode, and we will allow VLAN 50 on the trunk link.

Now that the interfaces are consistent and ready, let’s configure LACP EtherChannel step by step. You’ll define which interfaces participate in the bundle, assign their negotiation modes, and configure the logical Port-Channel as a trunk allowing VLAN 50.

Figure 3 – LACP Configuration Between Passive and Active Modes

Step 1 – Select the Interfaces

Begin by selecting the interfaces that will join the EtherChannel on each switch.
The interface range command allows you to configure multiple interfaces at once.

On SW1

SW1(config)# interface range g0/0 - 1

On SW2

SW2(config)# interface range g0/0 - 1

Once the correct interfaces are selected, you can enable LACP on each switch.

Step 2 – Assign LACP Modes

LACP uses two negotiation modes. For this configuration, SW1 will use Passive mode, while SW2 will use Active mode.
This combination allows one switch to initiate the negotiation while the other responds, forming the EtherChannel automatically.

Figure 4 – Setting LACP Mode: Passive and Active

SW1 (Passive Mode)

SW1(config-if-range)# channel-group 1 mode passive

SW2 (Active Mode):