Configuring Ironspan Features; Fast Port Span - Foundry Networks Switch and Router Installation And Configuration Manual

Foundry Switch and Router Installation and Configuration Guide
USING THE WEB MANAGEMENT INTERFACE
To display STP information for a specific VLAN:
1. Log on to the device using a valid user name and password for read-write access. The System configuration
panel is displayed.
2. Click on the plus sign next to Configure in the tree view.
3. Select the VLAN link to display the VLAN configuration options.
4. Select the Port link to display configuration information for the device's port-based VLANs. The STP state is
shown in the STP column.

Configuring IronSpan Features

This section describes how to configure the following features:
•

Fast Port Span

• Fast Uplink Span
• Single-instance STP
• Per VLAN Spanning Tree+ (PVST+) Compatibility
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.
• Fast Port Span eliminates unnecessary MAC cache aging that can be caused by topology change
notifications. Bridging devices age out the learned MAC addresses in their MAC caches if the addresses are
unrefreshed for a given period of time, sometimes called the MAC aging interval. When STP sends a
topology change notification, devices that receive the notification use the value of the STP forward delay to
quickly age out their MAC caches. For example, if a device's normal MAC aging interval is 5 minutes, the
aging interval changes temporarily to the value of the forward delay (for example, 15 seconds) in response to
an STP topology change.
In normal STP, the accelerated cache aging occurs even when a single host goes up or down. Because Fast
Port Span does not send a topology change notification when a host on a Fast Port Span port goes up or
down, the unnecessary cache aging that can occur in these circumstances under normal STP is eliminated.
Fast Port Span is a system-wide parameter and is enabled by default. Thus, when you boot a device with
software release 06.0.00 or later, all the ports that are attached only to end stations run Fast Port Span. For ports
that are not eligible for Fast Port Span, such as ports connected to other networking devices, the device
12 - 16 December 2000