LACP
acronymnetworking
Link Aggregation Control Protocol: bundles multiple physical links into one logical channel for bandwidth and redundancy, negotiated rather than hoped for.
IEEE 802.3ad/802.1AX; a bundle without negotiation is how you get one-sided port channels and mystery outages.
LACP bundles several physical links into one logical link, negotiating with the far end so both sides agree on membership rather than assuming it. The negotiation is the point: a static bundle configured differently at each end silently blackholes traffic, and LACP detects the mismatch and refuses to bring the link up.
The expectation it defeats is that four one-gigabit links give one four-gigabit link. They do not for a single flow, because packets in a conversation must stay ordered and therefore take one member link, chosen by a hash of addresses and ports. A bundle raises aggregate capacity across many flows and does nothing for one large transfer, which is why a backup job over a bundle runs at member speed and surprises people annually.