4. laruence Study Notes-generate tree STP

LAN (local area network)

Lan is interconnected through bridges. IEEE 802 standard has two bridge specifications, one defined by 802.1d.Transparent Bridge, The other is defined by 802.5.Source Route Bridge.

Bridge

Network Bridge, also known as Bridge,A network device,Responsible for network bridging. You can isolate collisions Based on Mac partition blocks. The bridge connects multiple network segments on the data link layer (OSI model layer 2nd ). The function of the bridge adapter is similar to that of other devices such as the hub used to connect to the network segment, but the latter works on the physical layer (OSI model layer 1st ).The bridge adapter forwards data to other networks only when data is transmitted between different networks.Not broadcast all data like a hub. For Ethernet, the term "bridging" officially refers to a device that complies with the IEEE 802.1d standard, that is, "network switching ". If there is a machine with frequent communication, it should be placed in the same zone; otherwise, the performance will be reduced. The bridge adapter can partition the network segment, not like the hub is still in the same collision domain name, so the bandwidth consumption is high. Because the Bridge uses its MAC table to prevent frame transmission from passing through, it is called a network component for data link layer operations.A switch is actually a multi-port bridge and a technology for Frame Forwarding.

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As shown in: When HOST 1 in the network needs to communicate with five hosts in the network, when host a sends a data frame (Data + The End Of The frame header frame, the frame header contains the target station address, and the end of the frame contains the source station address. When Port 1 reaches the bridge, the bridge finds the MAC address table (the MAC address of all hosts in the network) whether there is an address that needs to be forwarded, obviously, and then forwarded to host 5 through Port 2.

Spanning Tree

The spanning tree bridge is a transparent bridge that automatically selects routes without loading route tables or setting parameters.

STP (Spanning Tree Protocol) is a data link layer (Layer 2) communication protocol based on the OSI network model, used to ensure a non-circular local network environment.

Based on the algorithm prescribed by Radia Perlman during Dec operations, STP allows a network to be designed to contain standby (duplicate) connections so that when a line in operation fails, the backup path is provided automatically, and you need to eliminate the need to cause the bridge loop, manually start and close the backup connection. Therefore, STP can be used to prevent loops, MAC address fluctuations, repeated frames, and broadcast storms.

Broadcast storm

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Note:

Forwarding mechanism. Because the LAN is a group-based broadcast network, a port of the switch receives the broadcast. This switch has the responsibility to forward the broadcast through all other ports.

As shown in, When Xiao Zhang on the second floor of an apartment needs to communicate with Xiao Wang on the tenth floor of the apartment, the aggregation switch is a, the access switch is B on the left, and the access switch is C on the right, when the data sent by John passes through Switch B, switch B needs to forward the data to a and c, and switch C receives the data and forwards it to A and B, similarly, when a receives data, it forwards the data to B and C, so that the infinite loop goes down. Therefore, a clockwise and counterclockwise broadcast is formed, as shown in the figure on the right, when all members perform such broadcasts at the same time, a broadcast storm is formed, and the network is paralyzed.

Why do we need to add a link between the B switch and the C switch? Of course it is for security. If the links between A and B are interrupted, a will forward data through B without being affected. However, adding this link will cause a broadcast storm. How can this problem be avoided? There is always a way to do anything, that is, the spanning tree we want to talk about.Once a loop is found in the network, the switch automatically runs the Spanning Tree to block a port to eliminate the loop.

Practice 1

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: Create three vswitches. After the connection is successful, port F0/3 is blocked. This is the function of generating trees ~~

The STP process is as follows: first, the root bridge is elected based on the bridge ID generated by the combination of bridge priority and MAC address, the bridge with the smallest bridge ID will be the root bridge in the network ). On this basis, calculate the distance from each node to the root bridge, and obtain the cost of each redundant link from these paths. Select the minimum communication path (the corresponding port status changes to forwarding-forwarding ), the other is the backup path (the corresponding port status changes to blocking-blocking ). The communication task during STP generation is completed by the BPDU, which is divided into the configuration BPDU containing the configuration information (its size does not exceed 35b) and the notification BPDU that contains the topology change information (its length cannot exceed 4B ).

To be continued ~

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4. laruence Study Notes-generate tree STP