Chapter 4: Web management
NS3550-8T-2S Industrial Managed Switch User Manual
113
STP parameters
STP operation levels
The industrial managed 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. 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.
32768 + MAC
Priority
A relative priority for each switch – lower numbers give a
higher priority and a greater chance of a given switch
being elected as the root bridge
32768
Hello Time
The length of time between broadcasts of the hello
message by the switch
2 seconds
Maximum Age Timer
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 maximum age timer.
20 seconds
Forward Delay Timer
The amount of time spent by a port in the learning and
listening states waiting for a BPDU that may return the
port to the blocking state.
15 seconds
The following are the user-configurable STP parameters for the port or port group level:
Variable
Description
Default Value
Port Priority
A relative priority for each port – lower
numbers give a higher priority and a
greater chance of a given port being
elected as the root port
128
Port Cost
A value used by STP to evaluate paths –
STP calculates path costs and selects the
path with the minimum cost as the active
path
200,000-100Mbps Fast Ethernet ports
20,000-1000Mbps Gigabit Ethernet ports
0 - Auto
Default spanning-tree configuration
Feature
Default Value
Enable state
STP disabled for all ports
Port priority
128
