Technical data

Brocade MLX Series and NetIron Family Documentation Updates 49
53-1002805-03
STP feature configuration
1
STP feature configuration
TABLE 18 Feature support table
Spanning Tree Protocol (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 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 Brocade 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.
Features
supported
Brocade
NetIron XMR
Series
Brocade
MLX Series
Brocade
NetIron CES
2000 Series
BASE
package
Brocade
NetIron CES
2000 Series
ME_PREM
package
Brocade
NetIron CES
2000 Series
L3_PREM
package
Brocade
NetIron CER
2000 Series
BASE
package
Brocade
NetIron CER
2000 Series
Advanced
Services
package
Enhanced
support for
Fast Port
Span, Fast
Uplink Span,
and Single-
instance
Span
Yes Yes Yes Yes Yes Yes Yes