What does Passive mode in LACP do?

In Link Aggregation Control Protocol (LACP), when a device is set to Passive mode, it plays a more reactive role in the negotiation process for forming an EtherChannel. In this mode, the device will not actively initiate the negotiation; instead, it will respond to LACP packets that are received from another device configured to operate in Active mode.

When one end of the link is set to Active mode, it sends out LACP packets to find other links to aggregate. The device in Passive mode listens for these packets and only responds when it detects them. This behavior allows for the flexibility of having one side actively contribute to the negotiation while the other side stands by ready to join the negotiated link if prompted.

The functionality of Passive mode is particularly useful in scenarios where network configurations might require a more controlled method of negotiation, allowing for one end to dictate the formation of the link while the other end simply conforms to this setup.