8-port Gigabit Ethernet Switch User’s Guide
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This automatic network reconfiguration provides maximum uptime to network users. However, the concepts of the
Spanning Tree Algorithm and protocol are a complicated and complex subject and must be fully researched and
understood. It is possible to cause serious degradation of the performance of the network if the Spanning Tree is incorrectly
configured. Please read the following before making any changes from the default values.
The DGS-3308 STP allows two levels of spanning trees to be configured. The first level constructs a spanning tree on the
links between switches. This is referred to as the
Switch
or
Global
level. The second level is on a port group basis.
Groups of ports are configured as being members of a spanning tree and the algorithm and protocol are applied to the
group of ports. This is referred to as the
Port
or
VLAN
level
.
The Switch STP performs the following functions:
•
Creates a single spanning tree from any combination of switching or bridging elements.
•
Creates multiple spanning trees – from any combination of ports contained within a single switch, in user-
specified groups.
•
Automatically reconfigures the spanning tree to compensate for the failure, addition, or removal of any
element in the tree.
•
Reconfigures the spanning tree without operator intervention.
STP Operation Levels
The Switch allows for two levels of operation: the switch level and the port level. The switch level forms a spanning tree
consisting of links between one or more switches. The port level constructs a spanning tree consisting of groups of one or
more ports. The STP operates in much the same way for both levels.
Note:
On the switch level, STP calculates the Bridge Identifier for each switch and then sets the Root Bridge
and the Designated Bridges.
Note:
On the port level, STP sets the Root Port and the Designated Ports.
The following are the user-configurable STP parameters for the switch level:
Parameter
Description
Default
Value
Bridge Identifier
(Not user-
configurable
except by setting
priority below)
A combination of the User-set
priority and the switch’s MAC
address. The Bridge
Identifier consists of two
parts: a 16-bit priority and a
48-bit Ethernet MAC address
32768 + MAC
Priority
A relative priority for each
switch – lower numbers give
a higher priority and a
32768
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