782 Configuring Link AggregationFigure 28-1 shows an example of a switch in the wiring closet connected to aswitch in the data center by a LAG that consists of four physical 10 Gbpslinks. The LAG provides full-duplex bandwidth of 40 Gbps between the twoswitches.Figure 28-1. LAG ConfigurationWhy Are Link Aggregation Groups Necessary?The primary purpose of LAGs is to increase the overall bandwidth betweentwo switches. This is accomplished by effectively aggregating multiple portstogether that act as a single, logical connection between the two switches.LAGs also provide redundancy. If a link fails, traffic is automaticallyredistributed across the remaining links.What Is the Difference Between Static and Dynamic Link Aggregation?Link aggregation can be configured as either dynamic or static. Dynamicconfiguration is supported using the IEEE 802.3ad standard, which is knownas Link Aggregation Control Protocol (LACP). Static configuration is usedwhen connecting a PowerConnect 8000-series and 8100-series switches to anexternal Gigabit Ethernet switch that does not support LACP.One advantage of LACP is that the protocol enables the switch to confirmthat the external switch is also configured for link aggregation. When usingstatic configuration, a cabling or configuration mistake involving the 8000-series and 8100-series switch or the external switch could go undetected andthus cause undesirable network behavior. Both static and dynamic LAGs (viaLACP) can detect physical link failures within the LAG and continueforwarding 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.Wiring Closet Switch Data Center SwitchLAG
