How a vswitch works

Exchange Technology is a simplified, low-cost, high-performance, and high-port intensive exchange product. It reflects the second-layer operations of complex exchange technology in the OSI reference model. The difference with the bridge adapter is that the forwarding delay of the switch is very small, and the operation is close to the performance of a single LAN, far exceeding the forwarding performance between common bridging Internet.
The exchange technology allows the shared-bandwidth and dedicated LAN segments to adjust the bandwidth to reduce the bottleneck of information flow between the LAN. Now there are Ethernet, fast Ethernet, FDDI and ATM exchange products.
Three exchange technologies
Port Switching
Port switching technology first appeared in a slot hub. The backboards of these hubs are usually divided into multiple Ethernet segments, which do not need to be connected by bridges or routers. After the Ethernet main module is inserted, it is usually allocated to the network segment of a backboard. Port switching is used to allocate and balance the ports of the Ethernet module among multiple network segments on the backbench. Based on the degree of support, the port can also be subdivided:
* Module switching: migrate the entire module's network segment
* Port group switch: ports on the module are usually divided into several groups, and each group of ports allows network segment migration.
* Port-level switch: each port can be migrated between different network segments. This switching technology is based on the first layer of OSI and has the flexibility and load balancing capabilities. if properly configured, fault tolerance can still be implemented to a certain extent, but the features of shared transmission media are not changed, so it cannot be called a real exchange.
Frame Switching
Frame switching is currently the most widely used LAN switching technology. It provides a mechanism for parallel transmission by performing differential segments on Traditional transmission media to reduce conflicting domains and obtain high bandwidth. in general, each company's product implementation technology is different, but there are several ways to handle network frames:
* True-to-pass switching: Provides line rate processing capabilities. The switch reads only the first 14 bytes of the network frame and transfers the network frame to the corresponding fracture.
* Storage and forwarding: checks and controls the reading of network frames.
The exchange speed of the previous method is very fast, but it lacks more advanced control over network frames, lacks Intelligence and Security, and cannot support port exchange with different rates. therefore, each vendor focuses on the latter technology.

Cell Switch
The ATM technology represents a "good medicine" for the network and communication difficulties ". ATM uses a fixed length of 53 bytes of Cell Exchange. because the length is fixed, it is easy to implement with hardware. the ATM uses dedicated non-differential connections and runs in parallel. multiple nodes can be established through a vswitch at the same time, but the communication capability between each node is not affected. ATM also allows communication between the source and target nodes. the statistical time-division circuit is used in ATM, which can greatly improve the high-pass moral utilization rate. the bandwidth of an ATM can reach 25 M, 155 M, M, or even several GB of forwarding capacity.

LAN switch type and selection

LAN switches can be divided:
* Ethernet Switch
* Ring switch
* FDDI Switch
* ATM Switch
* Fast Ethernet Switch

Divided by the switch application field, it can be divided:
* Vswitch
* Workgroup Switch
* Trunk Switch
* Enterprise vswitches
* Segment Switch
* Port switch
* Network switch

Lan computers are the core devices that make up network systems. For users, the main indicators of LAN switches are port configuration, data, data exchange capability, Packet Exchange speed, and other factors. Therefore, note the following when selecting a vswitch:
1. Number of switch ports
2. Switch Port Model
3. system expansion capability
4. Connection Methods of Trunk Lines
5. Total switch switching capability
6. Whether route selection is required
7. Whether hot switching is required
8. Whether fault tolerance is required
9. compatibility with existing devices and smooth connection
10. network management capability

Stackable switches have the advantages of rapid deployment, good value, scalability, and ease of management. They are widely used, especially in e-commerce applications. However, evaluating a stackable switch based entirely on the price of each user port does not reflect all situations. In fact, if the vendor calculates the price per port based on the configuration that does not meet the actual conditions or makes other assertions, it may mislead users to judge a product based on the price.
The more comprehensive evaluation of Stackable switches is to increase the evaluation of scalability and manageability. When talking about scalability, many vendors list the number of user ports to support their high-reliability assurance. This is not enough. We also need to consider whether such configuration has an uplink, you also need to determine where the switch is blocked or saturated. There are three considerations:

Internal Scalability: to what extent does the interconnection between stack devices limit scalability?

Bandwidth expansion: How many ports can be upgraded from 10 Mbps Ethernet to Mbps Ethernet port before the switch is overloaded?

External Scalability: to what extent does a vswitch uplink limit the data streams transmitted to other parts of the network?

Take a vswitch with 24 user ports as an example. Here we intentionally use the word "User port", because in actual configuration, a certain number of ports have been used for server or internal and external connections. If the 24 ports have 10 Mbps throughput and the stackable device is connected to a Gigabit Ethernet uplink, then, upgrading eight ports to 100 Mbps Ethernet will make the uplink saturated.

The calculation process is as follows: 8 800 Mbps ports are equal to Mbps throughput, while the remaining 16 10 Mbps ports are equal to Mbps throughput. A total throughput of 960 Mbps means that further rapid Ethernet upgrades cannot be implemented without blocking the 1 Gbps uplink.

In addition, many 3rd-layer stackable switches do not support differentiated services, service types, or multi-protocol tag switching, therefore, this type of Stackable switch requires an external router or an additional 3rd-layer switch to obtain the required management features.

Manageability

Many studies have demonstrated that the costs involved in operation and management cost more in the life of the product than the initial purchase cost of the product. Therefore, manageability is another key factor in evaluating the overall value.

The inherent advantage of a stackable switch is that it is easier to manage a single logical entity than to manage multiple devices that must be configured and monitored independently. However, there are still some other factors that need to be studied, including the service quality QoS for priority data streams), the ability to execute policies, the ability to manage VLAN transmission streams, and ease of management and operation.

QoS features focus on saving the required bandwidth and forwarding the transmission stream to support the needs of different service levels. Generally, stackable switches support IEEE 802.1p and 802.1Q standards that describe the priority and VLAN. However, when it comes to the support for the resource retention protocol used to reserve the specified bandwidth for a specific data stream), the results are different, resource Reservation is indispensable to ensure that sufficient bandwidth is available during connection establishment.

Policy support

A policy is a rule that controls the behavior of a vswitch. The Network Administrator uses the policy to allocate bandwidth, priority, and control network access to the application stream, the focus is on the bandwidth management policies required to meet the service level agreement and the method of publishing policies to the switch. Configuring a vswitch at a time requires a lot of manpower and may cause input errors. Therefore, the policy must be published to the vswitch group. When a new policy is required, a large number of switches should be quickly modified. Therefore, you need to check whether the stackable switch supports the directory enable network and light Directory Access Protocol, and General Open Policy Service (a protocol with more features to be implemented ).

You can use VLANs to manage transmission streams across multiple switches or stacked devices. Currently, all products support 802.1Q-defined VLANs. Many products also support other VLANs Based on vswitch ports, Media Access Control addresses, layer-3rd protocols, or policies.