Switch Level STP
The switch STP parameters listed here can be configured by the user:
| Parameter |
| Description |
| Default Value |
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| Bridge Identifier |
| A combination of the |
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| (Not user- |
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| switch’s MAC address. The Bridge Identifier |
| 32768 + MAC |
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| configurable except |
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| consists of two parts: a |
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| by setting priority |
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| Ethernet MAC address |
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| below) |
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| Priority |
| A relative priority for each switch – lower numbers | 32768 |
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| give a higher priority and a greater chance of a |
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| given switch being elected as the root bridge |
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| Hello Time |
| The length of time between broadcasts of the hello |
| 2 seconds |
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| message by the switch |
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| Maximum Age |
| Measures the age of a received BPDU for a port |
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| and ensures that the BPDU is discarded when its |
| 20 seconds |
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| Timer |
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| age exceeds the value of the maximum age timer. |
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| Forward Delay |
| The amount time spent by a port in the learning |
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| and listening states waiting for a BPDU that may |
| 15 seconds |
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| Timer |
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| return the port to the blocking state. |
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Port Level STP
The VLAN or port STP parameters listed here may be configured by the user:
| Variable |
| Description |
| Default Value |
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| Port Priority |
| A relative priority for each port – lower numbers |
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| give a higher priority and a greater chance of a | 32768 |
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| given port being elected as the root port |
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| Port Cost |
| A value used by STP to evaluate paths – STP |
| 10 – 100Mbps Fast |
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| calculates path costs and selects the path with the |
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| Ethernet ports |
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| minimum cost as the active path. |
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Bridge Protocol Data Units
The Switch uses the following information for STP to stabilize network topology:
-The unique switch identifier
-The path cost to the root associated with each switch port
-The port identifier
This STP information is shared among 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
-The port identifier of the transmitting port
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