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Configuring Ethernet link aggregation
Overview
Ethernet link aggregation, or simply link aggregation, combines multiple physical Ethernet ports into one
logical link, called an "aggregate link." Link aggregation delivers the following benefits:
•
Increases bandwidth beyond the limits of any single link. In an aggregate link, traffic is distributed
across the member ports.
•
Improves link reliability. The member ports dynamically back up one another. When a member port
fails, its traffic is automatically switched to other member ports.
As shown in
, Device A and Device B are connected by three physical Ethernet links. These
physical Ethernet links are combined into an aggregate link, Link Aggregation 1. The bandwidth of this
aggregate link is as high as the total bandwidth of the three physical Ethernet links. At the same time, the
three Ethernet links back up one another.
Figure 10
Ethernet link aggregation
Basic concepts
Aggregation group, member port, and aggregate interface
Link aggregation is implemented by combining Ethernet interfaces into a link aggregation group. Each
link aggregation group has one logical aggregate interface. To an upper layer entity that uses the link
aggregation service, a link aggregation group appears to be a single logical link and data traffic is
transmitted through the aggregate interface. The rate of an aggregate interface equals the total rate of
its member ports in the Selected state, and its duplex mode is the same as the selected member ports. For
more information about the states of member ports in an aggregation group, see "
member ports in an aggregation group
Aggregate interfaces are one of the following types:
Bridge-aggregation (BAGG) interfaces
—Also called Layer 2 aggregate interfaces.
Route-aggregation (RAGG) interfaces
—Also called Layer 3 aggregate interfaces.
When you create an aggregate interface, the switch automatically creates an aggregation group of the
same type and number as the aggregate interface. For example, when you create interface
Bridge-Aggregation 1, Layer 2 aggregation group 1 is automatically created.
You can assign Layer 2 Ethernet interfaces only to a Layer 2 aggregation group, and Layer 3 Ethernet
interfaces only to a Layer 3 aggregation group.
Aggregation states of member ports in an aggregation group
A member port in an aggregation group can be in either of the following aggregation states:
•
Selected: A Selected port can forward user traffic.
