• Assign all ports in the EtherChannel to the same VLAN, or configure them as trunks. Ports with different native VLANs cannot form an EtherChannel. • An EtherChannel supports the same allowed range of VLANs on all the ports in a trunking Layer 2 EtherChannel. If the allowed range of VLANs is not the same, the ports do not form an EtherChannel even when PAgP is set to the auto or desirable mode. • Ports with different spanning-tree path costs can form an EtherChannel if they are otherwise compatibly configured. Setting different spanning-tree path costs does not, by itself, make ports incompatible for the formation of an EtherChannel.
Layer 3 EtherChannel Configuration Guidelines For Layer 3 EtherChannels, assign the Layer 3 address to the port-channel logical interface, not to the physical ports in the channel. Auto-LAG The auto-LAG feature provides the ability to auto create EtherChannels on ports that are connected to a switch. By default, auto-LAG is disabled globally and is enabled on all port interfaces. The auto-LAG applies to a switch only when it is enabled globally. On enabling auto-LAG globally, the following scenarios are possible: • All port interfaces participate in creation of auto EtherChannels provided the partner port interfaces have EtherChannel configured on them.
For more information, see the "The supported auto-LAG configurations between the actor and partner devices" table below. • Ports that are already part of manual EtherChannels cannot participate in creation of auto EtherChannels. • When auto-LAG is disabled on a port interface that is already a part of an auto created EtherChannel, the port interface unbundles from the auto EtherChannel. The following table shows the supported auto-LAG configurations between the actor and partner devices: Table 4: The supported auto-LAG configurations between the actor and partner devices On disabling auto-LAG globally, all auto created Etherchannels become manual EtherChannels.
You cannot add any configurations in an existing auto created EtherChannel. To add, you should first convert it into a manual EtherChannel by executing the port-channel persistent . Auto-LAG uses the LACP protocol to create auto EtherChannel. Only one EtherChannel can be automatically created with the unique partner devices. Note Configuring EtherChannels Layer 3 EtherChannel Configuration Guidelines Actor/Partner Active Passive Auto Active Yes Yes Yes Passive Yes No Yes Auto Yes Yes Yes Configuring EtherChannels 12