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Chapter 7 Spanning Tree
Management
Spanning Tree Management
This section describes the Spanning Tree Protocol (STP) (IEEE802 .1D and
IEEE802 .1Q) and covers the following topics:
•
Overview
Spanning Tree
•
•
STP Interfaces
RSTP Interfaces
•
Overview
STP protects a Layer 2 broadcast domain from broadcast storms by selectively
setting links to standby mode to prevent loops . In standby mode, these links
temporarily stop transferring user data . After the topology changes so that the
data transfer is made possible, the links are automatically re-activated .
Loops occur when alternate routes exist between hosts . Loops in an extended
network can cause switches to forward traffic indefinitely, resulting in increased
traffic load and reduced network efficiency .
STP provides a tree topology for any arrangement of switches and interconnecting
links, by creating a unique path between end stations on a network, and thereby
eliminating loops .
The device supports the following Spanning Tree Protocol versions:
•
Classic STP – Provides a single path between any two end stations, avoiding
and eliminating loops .
Chapter 7 Spanning Tree Management
•
Rapid STP (RSTP) – Detects network topologies to provide faster convergence
of the spanning tree . This is most effective when the network topology
is naturally tree-structured, and therefore faster convergence might be
possible . RSTP is enabled by default .
Spanning Tree
The Spanning Tree page contains parameters for enabling STP or RSTP . Use
the STP Interface page and RSTP Interface page to configure ports with these
modes, respectively .
To set the STP status and global settings, do the following:
STEP 1 Click Configuration > Spanning Tree Management > Spanning Tree .
STEP 2 Enter the parameters .
Global Settings
Spanning Tree—Select to enable STP on the device .
•
•
Spanning Tree Mode—Select an STP mode—Classic STP or Rapid STP .
Path Cost Default Values—Selects the method used to assign default path
•
costs to the STP ports . The default path cost assigned to an interface varies
according to the selected method .
Short—Specifies the range 1 through 65,535 for port path costs .
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Long—Specifies the range 1 through 200,000,000 for port path costs .
BPDU Handling—Select how Bridge Protocol Data Unit (BPDU) packets are
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managed when STP is disabled on the port or the device . BPDUs are used to
transmit spanning tree information .
Filtering—Filters BPDU packets when Spanning Tree is disabled on an
•
interface .
Flooding—Floods BPDU packets when Spanning Tree is disabled on an
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interface .
Bridge Configuration
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Priority—Set the global priority value . The priority value influences the port
choice when a bridge has two ports connected in a loop . The priority is a
value from 0 to 240, set in increments of 16 .
•
Hello Time—Set the interval (in seconds) that a root bridge waits between
configuration messages .
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