Final answer:
The mode 'On' is used in EtherChannel configuration to force an interface into a port channel without exchanging aggregation protocol packets
Step-by-step explanation:
When EtherChannel is configured, the mode that will force an interface into a port channel without exchanging aggregation protocol packets is On. In this mode, no negotiation is needed to form the channel; both sides must be set to this mode manually to form the EtherChannel. Mode Auto and Desirable are used with PAgP, whereas Active is utilized with LACP, both of which require packet exchange to form a port channel.