What is Link Aggregation (LAG/LACP)?

Link Aggregation (also called bonding, trunking, or port-channel) combines multiple physical network links into a single logical link, providing increased bandwidth and redundancy. If one physical link fails, the others continue carrying traffic. LACP (Link Aggregation Control Protocol, IEEE 802.3ad) is the standard protocol for negotiating link aggregation — both sides dynamically negotiate which links to aggregate. Cisco calls it EtherChannel; Linux calls it bonding. Load balancing across member links uses a hash algorithm based on: source/destination MAC, IP addresses, or port numbers — ensuring related packets take the same path (to avoid out-of-order delivery). A 4-link 1 Gbps bundle theoretically provides 4 Gbps of aggregate bandwidth. Static LAG (without LACP) can be configured but has no dynamic negotiation. Link aggregation is widely used between switches, between servers and switches, and between routers, providing both bandwidth and redundancy without spanning tree involvement.