Configuring Ironspan Features; Fast Port Span; Fast Port Span - Foundry Networks FESX Manual

Foundry Configuration Guide for the FESX, FSX, and FWSX
The STP information is shown in bold type in this example.
Syntax: show interfaces [ethernet [<slotnum>/]<portnum>] | [loopback <num>] | [slot <slot-num>] | [ve <num>] |
[brief]
You also can display the STP states of all ports by entering a command such as the following, which uses the brief
parameter:
FastIron SuperX Router(config)# show interface brief
Port Link State
1/1 Down None
1/2 Down None
1/3 Down None
1/4 Down None
1/5 Down None
1/6 Down None
1/7 Down None
1/8 Down None
.
. some rows omitted for brevity
.
3/10 Down None
3/11 Up Forward
In the example above, only one port, 3/11, is forwarding traffic toward the root bridge.

Configuring IronSpan Features

IronSpan 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 IronSpan parameters on Foundry 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:
• 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 Foundry 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's topology.
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Dupl Speed Trunk Tag Priori MAC
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© Foundry Networks, Inc.
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December 2005