Link aggregation

In computer networking, the term link aggregation applies to various methods of combining () multiple network connections in parallel in order to increase throughput beyond what a single connection could sustain, and to provide redundancy in case one of the links should fail. A Link Aggregation Group (LAG) combines a number of physical ports together to make a single high-bandwidth data path, so as to implement the traffic load sharing among the member ports in the group and to enhance the connection reliability.

Other umbrella terms used to describe the method include port trunking,link bundling,Ethernet/network/NIC bonding, or NIC teaming. These umbrella terms encompass not only vendor-independent standards such as (LACP) for Ethernet defined in IEEE 802.1AX and IEEE 802.1aq or the previous IEEE 802.3ad, but also various proprietary solutions.

Network architects can implement aggregation at any of the lowest three layers of the OSI model.

Regardless of the layer on which aggregation occurs, it balances the network load across all links. Most methods provide failover as well.

Combining can either occur such that multiple interfaces share one logical address (i.e. IP) or one physical address (i.e. MAC address), or it allows each interface to have its own address. The former requires that both ends of a link use the same aggregation method, but has performance advantages over the latter.

Link aggregation addresses two problems with Ethernet connections: bandwidth limitations and lack of resilience.

With regard to the first issue: bandwidth requirements do not scale linearly. Ethernet bandwidths historically have increased tenfold each generation: 10 megabit/s, 100 Mbit/s, 1000 Mbit/s, 10,000 Mbit/s. If one started to bump into bandwidth ceilings, then the only option was to move to the next generation which could be cost prohibitive. An alternative solution, introduced by many of the network manufacturers in the early 1990s, is to combine two physical Ethernet links into one logical link via channel bonding. Most of these solutions required manual configuration and identical equipment on both sides of the aggregation.

...
Wikipedia