Concepts
In Figure 3-1, DeviceA and DeviceB are connected through three Ethernet physical links. These links bundle into a logical link, and their bandwidths are combined to form the total bandwidth of the logical link. The three physical Ethernet links provide backup for each other, improving reliability.
The link aggregation interface can be used as a common Ethernet interface to implement routing protocols and other services. Unlike a common Ethernet interface, the link aggregation interface needs to select one or more member interfaces to forward traffic.
Link aggregation concepts are described as follows:
Link aggregation, link aggregation group (LAG), and link aggregation interface
Link aggregation technology bundles a group of physical interfaces into a logical interface to increase bandwidth and improve reliability.
An LAG binds multiple Ethernet links.
Each LAG has one logical interface, that is, link aggregation interface or Eth-Trunk.
Member interface and member link
The interfaces that constitute an Eth-Trunk are member interfaces. A link corresponding to a member interface is a member link.
Active and inactive interfaces and links
There are two types of interfaces in a LAG: active interfaces that forward data and inactive interfaces that do not forward data.
The link connected to an active interface is the active link, and the link connected to an inactive interface is the inactive link.
Upper threshold for the number of active interfaces
When the number of active interfaces reaches this threshold, the bandwidth of the Eth-Trunk will not increase even if more member links go Up. This guarantees high network reliability. When the number of active member interfaces reaches the upper threshold, additional active member interfaces go Down.
For example, 8 fully-functioning member links bundle into an Eth-Trunk link, with each link providing a bandwidth of 1 Gbit/s. If the Eth-Trunk link only needs to provide a maximum bandwidth of 5 Gbit/s, you can set the maximum number of Up member links to 5 or larger. The remaining unselected links in Up state automatically enter the backup state, improving reliability.
The upper threshold for the number of active interfaces is inapplicable to the manual load balancing mode. For details about the manual load balancing mode, see Link Aggregation in Manual Load Balancing Mode.
Lower threshold for the number of active interfaces
When the number of active interfaces falls below the lower threshold, the Eth-Trunk goes Down. This guarantees the minimum available bandwidth for the Eth-Trunk.
For example, if the Eth-Trunk is required to provide a minimum bandwidth of 2 Gbit/s and each member link's bandwidth is 1 Gbit/s, the lower threshold must be set to 2 or larger.