792 Configuring Link Aggregation
Figure 28-1 shows an example of a switch in the wiring closet connected to a
switch in the data center by a LAG that consists of four physical 10 Gbps
links. The LAG provides full-duplex bandwidth of 40 Gbps between the two
switches.
Figure 28-1. LAG Configuration
Why Are Link Aggregation Groups Necessary?
The primary purpose of LAGs is to increase the overall bandwidth between
two switches. This is accomplished by effectively aggregating multiple ports
together that act as a single, logical connection between the two switches.
LAGs also provide redundancy. If a link fails, traffic is automatically
redistributed across the remaining links.
What Is the Difference Between Static and Dynamic Link Aggregation?
Link aggregation can be configured as either dynamic or static. Dynamic
configuration is supported using the IEEE 802.3ad standard, which is known
as Link Aggregation Control Protocol (LACP). Static configuration is used
when connecting a PowerConnect 8000/8100-series switch to an external
Gigabit Ethernet switch that does not support LACP.
One advantage of LACP is that the protocol enables the switch to confirm
that the external switch is also configured for link aggregation. When using
static configuration, a cabling or configuration mistake involving the 8000-
series and 8100-series switch or the external switch could go undetected and
thus cause undesirable network behavior. Both static and dynamic LAGs (via
LACP) can detect physical link failures within the LAG and continue
forwarding traffic through the other connected links within that same LAG.
LACP can also detect switch or port failures that do not result in loss of link.
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