Link Aggregation Control Protocol (LACP) is a protocol used to negotiate and maintain LAG connections. EtherChannel on Cisco devices can be configured to use LACP to negotiate and maintain aggregated bundles of physical links. LACP is defined within IEEE 802.3ad.
LACP can be configured on Cisco devices using the active or passive mode. At least one end of an LACP bundle must be configured as active in order for the aggregated link to form.
The other LAG protocol supported by Cisco devices is PAgP.