User`s guide

8-port Gigabit Ethernet Switch User’s Guide
30
greater chance of a given
switch being elected as the
root bridge
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 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
Table 5-7. STP Parameters – Switch Level
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
32768
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.
19 – 100Mbps
Fast Ethernet
ports
4 – 1000Mbps
Gigabit
Ethernet ports
Table 5-8. STP Parameters – Port Group Level
Bridge Protocol Data Units
For STP to arrive at a stable network topology, the following information is used:
• The unique switch identifier
• The path cost to the root associated with each switch port
• The port identifier
STP communicates between switches on the network using Bridge Protocol Data Units (BPDUs). Each BPDU contains the
following information:
• The unique identifier of the switch that the transmitting switch currently believes is the root switch
• The path cost to the root from the transmitting port