Dell PowerConnect 5548P System User's Manual page 24

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Fast Link
STP can take 30–60 seconds to converge. During this time, STP detects
possible loops, enabling time for status changes to propagate and for relevant
devices to respond. This period of 30-60 seconds is considered too long a
response time for many applications. The Fast Link option bypasses this
delay, and can be used in network topologies, where forwarding loops do not
occur.
For more information on enabling Fast Link for ports and LAGs, see "STP
Port Settings" on page 443 or "Static Addresses" on page 425.
IEEE 802.1w Rapid Spanning Tree
Spanning Tree takes 30–60 seconds for each host to decide whether its ports
are actively forwarding traffic. Rapid Spanning Tree (RSTP) detects uses of
network topologies to enable faster convergence, without creating forwarding
loops.
For more information, see "Spanning Tree" on page 435.
IEEE 802.1s Multiple Spanning Tree
Multiple Spanning Tree (MSTP) operation maps VLANs into STP instances.
MSTP provides a different load balancing scenario. Packets assigned to various
VLANs are transmitted along different paths within MSTP Regions (MST
Regions). Regions are one or more MSTP bridges by which frames can be
transmitted. The standard lets administrators assign VLAN traffic to
unique paths.
For more information, see "Spanning Tree" on page 435.
STP BPDU Guard
BPDU Guard is used as a security mechanism, to protect the network from
invalid configurations.
BPDU Guard is usually used either when fast link ports (ports connected to
clients) are enabled or when the STP feature is disabled. When it is enabled
on a port, the port is shut down if a BPDU message is received and an
appropriate SNMP trap is generated.
For more information, see "Spanning Tree" on page 435.
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Dell PowerConnect 55xx Systems User Guide