74 Switch FeaturesBridge Protocol Data Unit (BPDU) GuardSpanning Tree BPDU Guard is used to disable the port in case a new devicetries to enter the already existing topology of STP. Thus devices, which wereoriginally not a part of STP, are not allowed to influence the STP topology.BPDU FilteringWhen spanning tree is disabled on a port, the BPDU Filtering feature allowsBPDU packets received on that port to be dropped. Additionally, the BPDUFiltering feature prevents a port in Port Fast mode from sending and receivingBPDUs. A port in Port Fast mode is automatically placed in the forwardingstate when the link is up to increase convergence time.Link Aggregation FeaturesFor information about configuring link aggregation (port-channel) features,see "Configuring Link Aggregation" on page 781.Link AggregationUp to eight ports can combine to form a single Link Aggregated Group(LAG). This enables fault tolerance protection from physical link disruption,higher bandwidth connections and improved bandwidth granularity.Per IEEE 802.1AX, only links with the same operational characteristics, suchas speed and duplex setting, may be aggregated. PowerConnect switchesaggregate links only if they have the same operational speed and duplexsetting, as opposed to the configured speed and duplex setting. This allowsoperators to aggregate links that use auto negotiation to set values for speedand duplex. Dissimilar ports will not become active in the LAG if theiroperational settings do not match those of the first member of the LAG.PowerConnect switches also support setting the MTU on a LAG. When a linkbecomes active in a LAG, its MTU is dynamically changed to the LAG MTU.When the link leaves the LAG, its MTU reverts to the link setting.Link Aggregate Control Protocol (LACP)Link Aggregate Control Protocol (LACP) uses peer exchanges across links todetermine, on an ongoing basis, the aggregation capability of various links,and continuously provides the maximum level of aggregation capability
