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Chapter 4: Web-Based Management
The switch with the lowest Bridge ID (switch C) was elected the root bridge, and the
ports were selected to give a high port cost between switches B and C. The two
(optional) Gigabit ports (default port cost = 4) on switch A are connected to one
(optional) Gigabit port on both switch B and C. The redundant link between switch B
and C is deliberately chosen as a 100 Mbps Fast Ethernet link (default port cost = 19).
Gigabit ports could be used, but the port cost should be increased from the default to
ensure that the link between switch B and switch C is the blocked link.
STP Parameters
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.
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
A combination of the User-set priority and the
Bridge Identifier (Not
switch's MAC address.
user configurable
The Bridge Identifier consists of two parts:
except by setting
priority below)
a 16-bit priority and a 48-bit Ethernet MAC address
32768 + MAC.
A relative priority for each switch - lower numbers
Priority
give a higher priority and a greater chance of a given
switch being elected as the root bridge.
The length of time between broadcasts of the hello
Hello Time
message by the switch.
Measures the age of a received BPDU for a port and
Maximum Age Timer
ensures that the BPDU is discarded when its age
exceeds the value of the maximum age timer.
The amount time spent by a port in the learning and
Forward Delay Timer
listening states waiting for a BPDU that may return
the port to the blocking state.
88
GE-DS-82 and 82-PoE Ethernet Managed Switch User Manual
DEFAULT VALUE
32768 + MAC
32768
2 seconds
20 seconds
15 seconds
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