Shulou(Shulou.com)06/01 Report--

Ethernet and related concepts of STP

Related concepts of Ethernet / LAN (local area network):

Question:

The signal transmission distance is limited.

Solution:

Repeater-amplifies the electrical signal to extend the transmission distance of the information

Problems caused by repeaters:

Only 2 ports with few connected devices

Solution:

Hub-A multi-port repeater that can connect multiple devices

Problems with hubs:

The signals sent by different terminal devices will conflict.

Mitigation scheme for signal conflict:

CSMA/CD, with collision detection, carrier sense multiple access mechanism

Introduce new devices:

Bridge (bridge)-isolate collision domain

Question:

Bridge devices have fewer ports and can only connect 2 devices

Solution:

Introduce new devices:

Switch-a multi-port bridge that can be implemented

Isolation of conflict domain

STP spanning Tree Protocol problem in traditional switched networks: single point of failure

Solution:

Add redundant links

Add redundant Devic

First figure out how the loop is formed?

The questions that follow:

Data forwarding loop

The data that produces the loop will be continuously transmitted in the network, thus consuming

Link resources and device resources in the network

Solution:

Run the STP protocol on the switch

STP-spanning Tree Protocol; (802.1D)

-implement loop protection when there are redundant links;-implement BPDU-bridging protocol data unit-classify PVST\ RSTP\ MSTP

Working process:

1. Determine the role of the switch

Root switch

Non-root exchange

Principle: compare the BID (bridge ID) of each switch, the smaller the better

Composition:

Priority + MAC

Priority-default is 32768

MAC-MAC of the motherboard of the switch (base MAC)

View command: show version

2. Determine the port role

Root port-each non-root switch has only one port closest to the root switch

Designated port-there is a port closest to the root switch in each collision domain

Non-designated port-all other ports are called non-designated port

How to express "distance"? In STP, the distance of a path is represented by cost; for some links, there are default cost values: 10m-cost 100m-cost 19; 1G-cost 4; 10G-cost 2; BPDU-Root-ID / / indicates who the root switch is Cost / / indicates the distance from the switch sending the BPDU to the root switch BID / / indicates the name of the switch that sent the BPDU; Port-ID / / indicates the port on which the sending switch is sent;-composition: Port priority. Port number-priority default value is 128

3. Determine the port status

Disable / / is equivalent to shutdown, and the port cannot be used at this time

Listening / / listening, which listens for BPDU and is used to determine the port role

Learning / / learning, in which the MAC is learned, forming the MAC address table

Forwarding / / forwarding, that is, the final forwarding status of the port

(root port, designated port)

Block / / blocking, the port cannot send data at this time

(non-designated port)

4. How does the switch distinguish the BPDU of different VLAN:

We use the lower 12 bit of the 2-byte priority in BID as the

Vlan number

As a result, it is concluded that:

The priority field of the first two bytes, which is really used to indicate priority, is only 4.

Bit; for all, there can only be 16 priorities

However, when representing priority values, the following 12bit must be included.

At the same time, must be 0

That is, the priority of the STP for each switch is 0-15 to the power of 2 to 12.

Multiple, that is, a multiple of 4096

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