Appendix D. Understanding And Troubleshooting The Spanning Tree Protocol; Stp Operation Levels - IBM BladeCenter Installation And User Manual

Appendix D. Understanding and troubleshooting the Spanning
Tree Protocol
This appendix provide details about how the STP works and describes how to
troubleshoot it.

STP operation levels

STP calculates the bridge identifier (ID) for each switch and then sets the root
bridge and the designated bridges.
The following table shows the user-configurable STP parameters for the switch
level.
The following table shows the user-configurable STP port parameters for the switch
level.
© Copyright IBM Corp. 2002
Table 9. STP parameters -- switch level
Parameter Description
Bridge identifier A combination of the user-set priority and
the switch MAC address. The bridge
(Not user-configurable
identifier consists of two parts: a 16-bit
except by setting the
priority and a 48-bit Ethernet MAC address.
priority as described
in this table)
Priority A relative priority for each switch. Lower
numbers assign a higher priority and
increase the probability of a switch being
elected as the root bridge
Hello time The length of time between broadcasts of
the hello message by the switch
Maximum age timer Measures the age of a received bridge
protocol data unit (BPDU) for a port and
ensures that the BPDU is discarded when
its age exceeds the value of the maximum
age timer
Forward delay timer The amount time spent by a port in the
learning and listening states waiting for a
BPDU that might return the port to the
blocking state
Table 10. STP port parameters -- switch level
Variable Description
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.
Port cost A value used by STP to evaluate paths
Default value
32768 + MAC
32768
2 seconds
20 seconds
15 seconds
Default value
32768
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