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32 Intel® NetStructure™ ZT 8101 10/100 Ethernet Switch User’s Manual
Switch Management and Operating Concepts
• On the switch level, STP calculates the Bridge Identifier for each switch and then sets the Root
Bridge and the Designated Bridges.
• On the port level, STP sets the Root Port and the Designated Ports.
The factory default settings should cover the majority of installations. Setting up STP using values
other than the defaults can be complex. Therefore, we recommend that you keep the default factory
settings, and STP will automatically assign root bridges/ports and block loop connections.
Influencing STP to choose a particular switch as the root bridge using the Priority setting, or
influencing STP to choose a particular port to block using the Port Priority and Port Cost settings
is, however, relatively simple.
For example, if all switches have STP enabled with default settings, the switch with the lowest
MAC address in the network becomes the root switch. By increasing the priority (lowering the
priority number) of the best switch, STP can be forced to select the best switch as the root switch.
STP Parameters for the Switch Level
The following are the user-configurable STP parameters for the switch level.
Use the following formulas when setting these parameters:
• Max Age <= 2 x (Forward Delay -1 second)
• Max Age >= 2 x (Hello Time + 1 second)
Parameter Description Default Value
Bridge Identifier
Specifies the 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. The only portion that a user
can configure is the priority.
32768 + MAC address
Priority
Specifies the relative priority for each switch. Lower
numbers specify a higher priority and a greater chance
of a given switch being elected as the root bridge.
32768
Hello Time
Specifies the length of time between broadcasts of the
hello message by the switch. It can be set from 1 — 10
seconds. This interval is not used until the switch
becomes (if ever) the root bridge.
The Hello Time parameter cannot be longer than the
Max Age parameter.
2 seconds
Max Age
Measures the age of a received BPDU for a port, and
ensures that the BPDU is discarded when its age
exceeds the value of the Max Age parameter.
It can be set from 6—40 seconds.
20 seconds
Forward Delay
Specifies the time a port can remaining in the listening
state while moving from the blocking state to the
forwarding state.
It can be set from 4—30 seconds.
15 seconds