STP Spanning Tree

STP spanning tree protocol that's it. A circular structure is changed into a tree structure. Logically blocks some ports to form a logical tree structure.

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Spanning Tree algorithm

1. Select the root bridge

2. Select the root port

3. Select the specified port

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Select the root bridge

Select Root Bridge is based on bridge ID

Bridge ID = Bridge Priority + Bridge MAC address

Show Version//can view the MAC address of the switch itself//

Bridge ID is selected as the root bridge, that is, the bridge priority is small or the MAC address is small

Default Bridge priority is 32768

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Select the root port

The root port exists above the non-root bridge, and you need to select one root port on each non-root bridge.

The root port is selected based on:

1. Lowest root path cost to the root bridge

2. Direct-connected Bridge ID minimum

3. Port ID min//Port priority default is 128//

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Select the specified port

Basis

1. Low Root path cost

2. Minimum switch bridge ID located on

3. Minimum Port ID

The ports above the root bridge are the specified ports, because the root path cost of the root bridge port is minimal, which is 0.

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The switch directly exchanges information such as bridge ID, root path cost, and so on through the BPDU "Bridge Protocol Data Unit".

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Five STP states for switch ports

1. Disable//force close//

2. Block//Only accept bpdu//

3. Listening//Build activity topology//

4. Learn//construct bridge tables//

5. Forwarding//Sending or receiving data//

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The relationship between STP and VLAN

CST Universal spanning Tree of 1.IEEE.

The 2.ciss private pvst each VLAN spanning tree.

The 3.ciss private pvst+ enhances each VLAN spanning tree.

A 4.IEEE mst spanning tree.

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Disadvantages of Pvst

The utilization of the switch is higher for the spanning tree that is generated to maintain each VLAN.

To support BPDUs for each VLAN, more trunk line bandwidth is required.

Pvst is not compatible with CST.

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Pvst+ can be compatible with other manufacturers ' switches.

Pvst+ can achieve Network Load balancing.

Pvst+ can configure the speed port.

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pvst+ Configuration commands

In the global mode

Spanning-tree VLAN ID//enable spanning Tree//

Spanning-tree VLAN ID root primary|secondary//Specify root bridge, configure primary priority is 24576, configure secondary priority to 28672//

Spanning-tree VLAN ID cost port Costs//Modify port Cost//

Spanning-tree VLAN ID port-priority priority//Modify port Priority//

Spanning-tree Portfast//configuration speed port, general configuration on ACCSS link//

Show Spanning-tree//view spanning Tree//

Show Spanning-tree VLAN ID detail//View details about a VLAN//

STP Spanning Tree