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STP spanning tree is a two-layer network optimization technology, the main function is to redundancy and prevent the generation of loops.

The role of STP:

V logically disconnect the link to prevent the occurrence of network storm.

V when the line fails, the blocking interface is activated and communication is resumed.

BID: bridge ID,BID= priority + MAC address, switch default priority is 32768.

PID: Port ID,PID= port priority + port number, the default priority of the port is 128.

STP's election algorithm:

V electing the root switch: the root switch is elected according to BID, and the smaller the value is, the root switch is.

V electing the root port (RP): according to the path cost to the root switch, the peer BID and the peer PID elect the root port. The lower the value, the root port.

V elect designated port (DP): according to the path cost to the root switch, the local BID and the local PID elect the designated port. The lower the value, the root port.

V all other interfaces are blocked.

100MB link cost is 19.

1000MB link cost is 4

10000MB link cost is 2.

10MB link cost is 100

16MB link cost is 62

The cost of 45MB link is 39

155MB link cost is 14

622MB link cost is 6

The STP spanning tree uses BPDU bridging data units to communicate.

Type of BPDU:

V configuration BPDU: for spanning tree calculation, updated every 2 seconds.

V Topology change Communication: it is sent only when there is a problem with the network, which is used to notify the network change.

STP interface status:

V blocking (Blocking): the default delay is 20s and only BPDU is received.

V snooping (Listening): the default delay is 15s, the interface is enabled, and the active topology is built.

V learning (Learning): the default delay is 15s to build the MAC address table.

V forwarding (Forwarding): send and receive user data

V disable (Disabled): the interface shuts down Shutdwon.

STP uses three timing methods to ensure the convergence of the network:

V Hello time: the default time is 2s.

V forwarding delay: the default is 30s.

V maximum aging time: the default is 20s.

The relationship between STP and VLAN:

V IEEE CST generic spanning tree: do not consider the existence of VLAN, only generate a single STP in the network.

V IEEE's MST multiple spanning tree: multiple VLAN share a tree.

V CISCO PVST per VLAN spanning tree: one STP per VLAN.

V CISCO's PVST+ adds each VLAN spanning tree: one STP per VLAN, which is compatible with CST spanning tree.

PVST+ spanning tree command for CISCO:

Command

Description

(config) # spanning-tree vlan 10

Enable the STP function of VLAN10

(config) # spanning-tree vlan 10 priority 4096

Configure VLAN10 with a STP priority of 4096

(config) # spanning-tree vlan 10 root primary

Configure STP of VLAN10 as the primary root

(config) # spanning-tree vlan 10 root secondary

Configure STP of VLAN10 as secondary root

(config) # spanning-tree vlan 10 cost 19

Configure STP port cost for VLAN10

(config) # spanning-tree vlan 10 port-priorty 128

Configure the STP port priority of VLAN10 to 128,

(config-if) # spanning-tree portfast

Configure the interface as a fast interface

# show spanning-tree

View spanning tree status

# show spanning-tree blockedports

View spanning tree blocking

# show spanning-tree vlan 10 detail

View spanning tree VLAN10 details

Note: the speed interface is generally used in the PC interface, which can turn off the convergence of STP and achieve rapid communication.

The primary root priority defaults to 8192, and the secondary root priority defaults to 16384.

MSTP spanning tree multiple VLAN can share a spanning tree.

MSTP spanning tree introduces the concept of domain, in which there can be multiple instances in a domain, and one instance can be understood as a tree.

Instance 0 is a special tree that starts by default whenever MST is started, and it maps all VLAN to this instance by default.

BPDU protection: when the switching device starts BPDU protection, if the edge port receives another spanning tree BPDU, the edge port will automatically Shutdown.

Root protection: due to malicious * * in the network, the root bridge receives a higher priority BPDU, and the root port does not forward the message, and returns to normal state when the priority is restored.

Huawei H3C MSTP multiple spanning tree command:

Command

Description

[huawei] stp region-configuration

MSTP domain configuration

[huawei-mst-region] region-name RG1

MSTP domain name is RG1

[huawei-mst-region] instance 1 vlan1 to 10

Add VLAN1 to VLAN10 to instance 1

[huawei-mst-region] active region-configuration

Start domain configuration

[huawei] stp instance 1 priority 0

Configure spanning tree instance 1 with a priority of 0

[huawei] stp pathcost-standard legacy

Configure the port cost as Huawei private computing method

[huawei-Ethernet0/0/1] bpdu enable

Turn on the interface BPDU switch

[huawei-Ethernet0/0/1] stp root-protection

Interface initiates root guard

[huawei-Ethernet0/0/1] stp edged-port enable

Configure an interface as an edge interface (fast interface)

[huawei] stp enable

Open spanning tree

Note: instance: the meaning of an example.

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