5. desktop switches
A table-based switch is the most common low-end switch. It is different from other switches in that it supports a small number of MAC addresses per port. Generally, the number of ports is smaller than 12, but it is not absolute), only has the most basic switch features, of course, the price is also the cheapest.
Although this type of switch is the lowest in the entire switch, it still has the general superiority of the switch compared with the hub. Besides, many application environments only need the basic performance, therefore, it is widely used. It is mainly used for office desktops of small or medium-sized enterprises. In terms of transmission speed, most desktop switches currently provide multiple ports with 10/100 Mbps adaptive capability. Figure 10 shows two desktop switches of different brands.
Figure 10
4. Switch structure division
Based on the port structure of the vswitch, The vswitch can be roughly divided into two different structures: fixed port switch and modular switch. In fact, there is also a balance between the two, that is, a certain number of expansion slots or modules are provided on the basis of providing basic fixed ports.
1. Fixed port switch
As the name implies, the fixed port is fixed. If it is port 8, it can only have eight ports and cannot be added. 16 ports can only have 16 ports and cannot be expanded. Currently, vswitches with fixed ports are common and there is no clear rule on the number of ports. Generally, port 8, port 16, and port 24 are standard ports. But now the manufacturers have their own opinions. They think that the number of ports can be produced in the market. Currently, vswitch ports are relatively complex. The number of non-standard ports mainly includes four ports, five ports, 10 ports, 12 ports, 20 Ports, 22 ports, and 32 ports.
Although the fixed port switch is relatively cheaper, it can only provide limited ports and fixed interfaces. Therefore, regardless of the number of users that can be connected, it also has certain limitations in terms of available transmission media. However, this type of switch is widely used in working groups and is generally applicable to small networks and Desktop Exchange environments. 11. Figure 12 shows a vswitch with port 16 and port 24 respectively.
Figure 11
Figure 12
Because of its installation architecture, fixed port switches are divided into desktop switches and rack-mounted switches. Like hubs, rack-mounted switches are easier to manage and more suitable for large-scale networks. Their structures must comply with 19 inch international standards, it is used to install in a Cabinet together with other switching devices, routers, servers, and so on. Table-based switches can only provide a small number of ports and cannot be installed in cabinets. Therefore, they are generally used only for small networks. As shown in Figure 13 and figure 14, is a desktop fixed port switch suddenly changed to jiotan silk? Br>
Figure 13
Figure 14
2. modular Switch
Modular switches are much more expensive in terms of price, but with greater flexibility and scalability, users can choose any number of modules with different rates and different interface types, to meet ever-changing network needs. In addition, most chassis switches have strong fault tolerance capabilities, support redundant backup of switch modules, and often have hot swappable dual power supply to ensure the power supply of switches. When selecting a vswitch, you should select the chassis or fixed mode based on the needs and funding considerations. Generally, enterprise-level switches should consider their scalability, compatibility, and troubleshooting. Therefore, chassis switches should be selected, while backbone switches and working group switches should have a single task, therefore, a simple and clear fixed switch can be used. 15 is a modular, Fast Ethernet switch with four pluggable modules, which can be flexibly configured as needed.
Figure 15
5. Division based on the protocol layer of the switch
We know that all network devices work at a certain level of the OSI/RM open model. The higher the working level, the higher the technology of the devices, the better the performance, and the higher the grade. The same is true for switches. With the development of the exchange technology, switches have evolved from the Layer 2 that originally worked in OSI/RM to the fourth switch that can work now, therefore, the protocol layer switches can be divided into Layer 2 switches, Layer 3 switches, and Layer 4 switches.
1. Layer 2 Switch
The L2 Switch is defined at the second protocol layer of OSI/RM, because it can only work at the layer-data link layer of the OSI/RM open system model. The second layer switch relies on information in the link layer, such as the MAC address, to exchange the line rate between data on different ports. The main functions include physical addressing, error verification, frame sequence, and data flow control. This is the most primitive exchange technology product. Currently, table-based switches generally belong to this type, because table-based switches are generally not very complex and are at the most basic layer of the network, therefore, you only need to provide the most basic data link function. Currently, Layer 2 vswitches are most commonly used at a low price and meet the actual application requirements of small and medium-sized enterprises. These vswitches are generally used at the desktop level of small or medium-sized enterprises. As shown in Figure 16, it is a second-layer switch product. It should be noted that all switches are backward compatible at the protocol level, that is, all switches can work on the second layer.
Figure 16
2. layer-3 Switch
The third layer is also defined by the network layer, which corresponds to the OSI/RM open system model. That is to say, this type of switch can work at the network layer, which is more advanced than the second layer switch, enhanced functions. Because the layer-3 Switch works at the network layer of the OSI/RM model, it has the routing function. It provides IP address information to the network path selection and implements line rate exchange of data between different network segments. When the network size is large, it can be divided into small independent VLAN network segments according to special application requirements to reduce the impact of broadcast. Generally, these switches adopt a modular structure to meet the needs of flexible configuration. In large and medium-sized networks, layer-3 switches have become basic configuration devices. Figure 17 shows that 3COM is a layer-3 switch.
Figure 17
3. layer-4 Switch
The layer-4 switch is a switch product developed using the layer-4 switch technology. Of course, it works on the layer-4 of the OSI/RM model, that is, the transport layer, directly facing specific applications. The layer-4 switch supports various protocols, such as HTTP, FTP, Telnet, and SSL. Set up virtual IP addresses (VIP) for each server group for search in layer-4 Switching. Each group of servers supports an application. In the Domain Name Server DNS), the address of each application server stored is VIP, rather than the actual server address. When a user applies for an application, a VIP connection request with the target server group, such as a TCPSYN packet, is sent to the server switch. The server switch selects the best server in the group, replaces the VIP in the terminal address with the actual Server IP address, and sends the connection request to the server. In this way, all packets in the same range are mapped by the server switch and transmitted between the user and the same server. Shown in 18 is a layer-4 switch product. It can be seen that it also uses a module structure.
Figure 18
The layer-4 exchange technology has obvious advantages over the original layer-2 and layer-3 exchange technologies. From the operational perspective, the layer-4 exchange technology is stable, because it controls the packet in the range from the source end to the destination end. On the other hand, a vro or layer-3 Switch only processes a single package. It is unclear where the previous package came from or where the next package came from. They only detect the TCP port numbers in the packet header, establish a priority queue based on the application, and the router determines the packet route based on the links and available nodes of the Network; the layer-4 switch determines the interval based on the available servers and performance. Currently, because this exchange technology is not yet mature and expensive, layer-4 switches are rare in practical applications.
6. Based on whether the network management function is supported
If a vswitch supports network management, we can divide it into two categories: "Network Management" and "non-network management.
The job of a network-managed switch is to keep all network resources in a good state. Vswitch provides various network management methods, such as Console Based on the terminal control port, Web pages, and Telnet remote logon network. Therefore, the network administrator can perform local or remote real-time monitoring on the switch's working status and network running status, and manage the working status and mode of all switching ports globally. Vswitches support the SNMP protocol. The SNMP protocol is composed of a set of simple network communication specifications. It can complete all basic network management tasks and has fewer network resources and some security mechanisms ,. The working mechanism of the NMP protocol is very simple, and network information is exchanged mainly through various types of messages, namely, data units of the PDU protocol. However, vswitches are much more expensive than non-vswitches described below.
Vswitches use the embedded remote monitoring RMON) standard to track traffic and sessions, which is very effective for determining network bottlenecks and congestion points. The software agent supports four RMON group history, statistics, alarms, and events) to enhance traffic management, monitoring, and analysis. Statistics are general network traffic statistics, and historical statistics are network traffic statistics within a certain period of time. Alarms can be triggered when the preset limit value of network parameters is exceeded. Time indicates management events.
There are also vswitches that provide policy-based QoSQuality of service ). 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. Indicates the port status, half-duplex/full-duplex, and 10 BaseT/100BaseT multi-function light-emitting diode LEDs at each port of the switch), and indicates the system and redundant power supply RPS) A comprehensive and convenient visual management system is formed by switching status LEDs with bandwidth utilization. Currently, most branch-level switches are non-Network-managed. Only enterprise-level and a few branch-level switches support the network management function. Figure 19 shows two network-managed switch products.
Figure 19
We have introduced several mainstream classification methods of vswitches one by one. I believe you will have a basic and comprehensive understanding of the main types of vswitches. The next article will introduce the switch's main exchange technologies and precautions for purchase.
