What does the "On" mode indicate for PAgP?

The "On" mode for Port Aggregation Protocol (PAgP) indicates that the interface will not engage in any negotiation to form an EtherChannel. When an interface is configured in "On" mode, it assumes that an EtherChannel will be established without the need for any protocol exchanges or negotiation with the connected device. This means that the port will try to bundle with the other end immediately, expecting it to also be configured in a compatible mode (like "On") without the use of PAgP or any other negotiation mechanism.

In contrast to other modes, such as "Desirable" or "Auto," which involve negotiation, "On" mode simplifies the configuration by eliminating the need for any interaction or checks to determine if the other interface is ready to form an EtherChannel. This approach can lead to more straightforward setups but demands identical configurations on both ends to successfully create an EtherChannel, as there’s no fallback to handle mismatches.