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

 

 

Bridge Identifier (Not

A combination of the User-set priority and the

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.

 

 

Hello Time

The length of time between broadcasts of the hello

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.

 

 

DEFAULT VALUE

32768 + MAC

32768

2seconds

20seconds

15seconds

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GE-DS-82 and 82-PoE Ethernet Managed Switch User Manual

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GE GE-DS-82, 82-POE user manual STP Parameters, STP Operation Levels, Parameter Description, Default Value