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Network engineers must know: Causes and solutions of switch loops

Causes and solutions of switch loops

Causes and solutions of switch loops

The Internet age has had a huge impact on our lives and brought us a lot of convenience, but at the same time it has brought us many problems, such as network security.
Someone has said that in today’s network communication traffic, about 80% of the resources are wasted, and less than one-fifth of the resources are effectively used.
The anti-ring mechanism is the purification mechanism produced in such a bad environment.
Usually our network loop is divided into the second layer loop and the third layer loop. The formation of all loops is caused by confusion caused by the unclear destination path.
The second layer loop is what we call the switch loop, which is generated by the vicious circle of switch broadcast messages. We all know that the switch is connected to the main equipment connected to the LAN, and the switch divides the conflict domain, but does not divide the broadcast domain, so the switch allows to forward broadcast messages by default. And because of the working principle of the switch, when it is in the MAC table query, if the query fails, the data frame will be sent out from other ports except the receiving port. So when the switches are connected in a ring, a data frame will loop endlessly. At this time, the spanning tree we learned is produced to prevent loops in the switching network.

The original version of spanning tree is 802.1d, which is STP (Spanning Tree Protocol). The design of the 802.1D Spanning Tree Protocol (STP) standard in junior high school is that every time a connection is interrupted for about one minute and then restored, it can be considered as good performance. But the standard of this version is that all VLANs share a spanning tree, so it is also called CST (Common Spanning Tree).
Cisco enhanced the original 802.1D specification with functions such as Uplink Fast, Backbone Fast, and Port Fast in order to accelerate the convergence time of bridged networks. The disadvantage is that these mechanisms are proprietary and require additional configuration. That is, the Rapid Spanning Tree Protocol.
The Rapid Spanning Tree Protocol (RSTP, IEEE 802.1W) can be regarded as an evolution of the 802.1D standard, not just a revolution. The terminology in 802.1D remains basically unchanged. And most of the parameters have not changed, so users who are familiar with 802.1D can easily and quickly configure the new protocol. In most cases, the performance of RSTP is better than that of Cisco’s proprietary extensions, and no additional configuration is required.
Later, MSTP (802.1s) appeared. Multiple Spanning Tree Protocol is a spanning tree protocol defined in IEEE802.1s. By generating multiple spanning trees, the Ethernet loop problem is solved.
RSTP has been improved on the basis of STP to achieve rapid convergence of the network topology. However, RSTP and STP still have the same flaw: because all VLANs in the LAN share a spanning tree, it is impossible to achieve load balancing of data traffic between VLANs. After the link is blocked, no traffic will be carried, and some may be caused. VLAN packets cannot be forwarded.
In order to make up for the shortcomings of STP and RSTP, the 802.1S standard released by IEEE in 2002 defines MSTP. MSTP is compatible with STP and RSTP, can converge quickly, and provides multiple redundant paths for data forwarding, and achieves load balancing of VLAN data during data forwarding.
MSTP divides a switching network into multiple domains, and multiple spanning trees are formed in each domain, and the spanning trees are independent of each other. Each spanning tree is called a Multiple Spanning Tree Instance (MSTI), and each domain is called an MST domain.
The so-called spanning tree instance is a collection of multiple VLANs. By bundling multiple VLANs into one instance, communication overhead and resource occupancy can be saved. The calculation of the topology of each MSTP instance is independent of each other, and load balancing can be achieved on these instances. Multiple VLANs with the same topology can be mapped to an instance. The forwarding status of these VLANs on the port depends on the status of the port in the corresponding MSTP instance.

Causes and solutions of switch loops

The Internet age has had a huge impact on our lives and brought us a lot of convenience, but at the same time it has brought us many problems, such as network security.
Someone has said that in today’s network communication traffic, about 80% of the resources are wasted, and less than one-fifth of the resources are effectively used.
The anti-ring mechanism is the purification mechanism produced in such a bad environment.
Usually our network loop is divided into the second layer loop and the third layer loop. The formation of all loops is caused by confusion caused by the unclear destination path.
The second layer loop is what we call the switch loop, which is generated by the vicious circle of switch broadcast messages. We all know that the switch is connected to the main equipment connected to the LAN, and the switch divides the conflict domain, but does not divide the broadcast domain, so the switch allows to forward broadcast messages by default. And because of the working principle of the switch, when it is in the MAC table query, if the query fails, the data frame will be sent out from other ports except the receiving port. So when the switches are connected in a ring, a data frame will loop endlessly. At this time, the spanning tree we learned is produced to prevent loops in the switching network.

The original version of spanning tree is 802.1d, which is STP (Spanning Tree Protocol). The design of the 802.1D Spanning Tree Protocol (STP) standard in junior high school is that every time a connection is interrupted for about one minute and then restored, it can be considered as good performance. But the standard of this version is that all VLANs share a spanning tree, so it is also called CST (Common Spanning Tree).
Cisco enhanced the original 802.1D specification with functions such as Uplink Fast, Backbone Fast, and Port Fast in order to accelerate the convergence time of bridged networks. The disadvantage is that these mechanisms are proprietary and require additional configuration. That is, the Rapid Spanning Tree Protocol.
The Rapid Spanning Tree Protocol (RSTP, IEEE 802.1W) can be regarded as an evolution of the 802.1D standard, not just a revolution. The terminology in 802.1D remains basically unchanged. And most of the parameters have not changed, so users who are familiar with 802.1D can easily and quickly configure the new protocol. In most cases, the performance of RSTP is better than that of Cisco’s proprietary extensions, and no additional configuration is required.
Later, MSTP (802.1s) appeared. Multiple Spanning Tree Protocol is a spanning tree protocol defined in IEEE802.1s. By generating multiple spanning trees, the Ethernet loop problem is solved.
RSTP has been improved on the basis of STP to achieve rapid convergence of the network topology. However, RSTP and STP still have the same flaw: because all VLANs in the LAN share a spanning tree, it is impossible to achieve load balancing of data traffic between VLANs. After the link is blocked, no traffic will be carried, and some may be caused. VLAN packets cannot be forwarded.
In order to make up for the shortcomings of STP and RSTP, the 802.1S standard released by IEEE in 2002 defines MSTP. MSTP is compatible with STP and RSTP, can converge quickly, and provides multiple redundant paths for data forwarding, and achieves load balancing of VLAN data during data forwarding.
MSTP divides a switching network into multiple domains, and multiple spanning trees are formed in each domain, and the spanning trees are independent of each other. Each spanning tree is called a Multiple Spanning Tree Instance (MSTI), and each domain is called an MST domain.
The so-called spanning tree instance is a collection of multiple VLANs. By bundling multiple VLANs into one instance, communication overhead and resource occupancy can be saved. The calculation of the topology of each MSTP instance is independent of each other, and load balancing can be achieved on these instances. Multiple VLANs with the same topology can be mapped to an instance. The forwarding status of these VLANs on the port depends on the status of the port in the corresponding MSTP instance.

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