Configure an EtherChannel by first defining the requirements and the goal you want to achieve and then applying the appropriate commands on your devices between which the logical interface will be deployed.
The following steps need to be performed to implement EtherChannel between two switches:
- Determine the number of physical links to be bundled into an EtherChannel and their characteristics, such as speed, duplex mode, and VLAN membership.
- Configure the switches for static EtherChannel or enable PAgP or LACP for dynamic EtherChannel.
- Configure the EtherChannel interface with the same parameters on both switches.
- Verify the EtherChannel configuration by checking the status of the EtherChannel interface.
Let's use the example topology in the image above to understand exactly how to configure EtherChannel. The goal is to implement Layer 2 EtherChannel between the two switches (SW1 and SW2) by bundling the four FastEthernet interfaces on each device.
Use “channel-group channel-group-number mode desired-mode” to bundle the physical interfaces into an EtherChannel. The channel group number identifies the EtherChannel locally on the devices, while the mode defines how the EtherChannel will be built. Use “interface port-channel channel-group-number” to access the EtherChannel mode.
In our configuration example, let us assume that all physical interfaces are already preconfigured with the same parameters on both switches.
As you can see from the commands above, it is recommended that you shut down all physical interfaces first so you do not experience any unexpected behavior during the EtherChannel implementation.
Then, you bundle them into a logical interface port channel 1 (it can be any number) by using the "channel-group" command and assign the desired mode (active mode in our case, which means that LACP will be used).
Once configured, you can access the port channel and configure it as any other physical interface on the switch (configured as a trunk in the example). Finally, you need to enable the physical interfaces so the EtherChannel can start functioning.
The configuration on SW2 would be identical to the one on SW1. However, if desired, you can use a different port channel ID (recommended to be the same for easier management) and the same or a different mode (passive instead of active).
To verify the EtherChannel configuration and its operability, you can use the following two commands:
- Show etherchannel summary
- Show etherchannel port-channel channel-group-number
Now, suppose you want to create a Layer 3 EtherChannel. In this case, you must change the operational mode on the physical interfaces (assuming the switch is L3) from Layer 2 to Layer 3 by using the "no switchport" command.
After that, as a Layer 3 EtherChannel (you must use the same "no switchport" command for the logical interface), you can apply an IP address or any other Layer 3 parameter on the Layer 3 port channel.
The following example shows the configuration of a Layer 3 EtherChannel:
