Configuring Stp Related Features; Fast Port Span - Dell PowerConnect B-FCXs Configuration Manual

PowerConnect#show interface brief
Port
1/1
1/2
1/3
1/4
1/5
1/6
1/7
1/8
.
. some rows omitted for brevity
.
3/10
3/11
In the example above, only one port, 3/11, is forwarding traffic toward the root bridge.

Configuring STP related features

STP features extend the operation of standard STP, enabling you to fine tune standard STP and
avoid some of its limitations.
This section describes how to configure these parameters on Layer 3 Switches using the CLI.

Fast port span

When STP is running on a device, message forwarding is delayed during the spanning tree
recalculation period following a topology change. The STP forward delay parameter specifies the
period of time a bridge waits before forwarding data packets. The forward delay controls the
listening and learning periods of STP reconvergence. You can configure the forward delay to a
value from 4 – 30 seconds. The default is 15 seconds. Thus, using the standard forward delay,
convergence requires 30 seconds (15 seconds for listening and an additional 15 seconds for
learning) when the default value is used.
This slow convergence is undesirable and unnecessary in some circumstances. The Fast Port
Span feature allows certain ports to enter the forwarding state in four seconds. Specifically, Fast
Port Span allows faster convergence on ports that are attached to end stations and thus do not
present the potential to cause Layer 2 forwarding loops. Because the end stations cannot cause
forwarding loops, they can safely go through the STP state changes (blocking to listening to learning
to forwarding) more quickly than is allowed by the standard STP convergence time. Fast Port Span
performs the convergence on these ports in four seconds (two seconds for listening and two
seconds for learning).
In addition, Fast Port Span enhances overall network performance in the following ways:
•
PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Link State Dupl Speed Trunk Tag Priori MAC
Down None None None
Down None None None
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Down None None None
Down None None None
Down None None None
Down None None None
Up Forward Full 100M
Fast Port Span reduces the number of STP topology change notifications on the network.
When an end station attached to a Fast Span port comes up or down, the Dell PowerConnect
device does not generate a topology change notification for the port. In this situation, the
notification is unnecessary since a change in the state of the host does not affect the network
topology.
Configuring STP related features
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