Switch working principle and Spanning Tree Protocol principle

The processing speed of the switch itself can reach a very high level. Users are often superstitious about the Gbps-level high-speed backplane. In fact, this is a misunderstanding. The network used by workstations or servers connected to the access network is a large network, which follows the CSMA/CD media access rules.

In the current customer/Server mode, multiple workstations access the server at the same time, so it is very easy to form a server bottleneck. Some vendors have designed one or more high-speed ports in the vswitch (for example, one or two Mbps ports can be configured for Linkswitch1000 of 3COM ).

It is convenient for users to connect to the server or high-speed backbone network. You can also design multiple servers (for Business Division) or append multiple NICs to eliminate the bottleneck. The switch also supports Spanning Tree algorithms to facilitate fault-tolerant Redundant connections in your architecture.

1. Broadcast frames in the Network

Currently, Netware and Windows NT are widely used network operating systems, while Lan Server servers provide services to clients by sending network broadcast frames. The existence of broadcast packets in these LAN greatly reduces the efficiency of the switch. In this case, you can use the virtual network function of the switch (not all vswitches support the virtual network) to limit the broadcast packets to a certain range.

The ports of each vswitch support a certain number of MAC addresses, so that the vswitch can "remember" The status of a group of connected sites on this port, the number of MAC ports supported by different vswitch ports provided by the manufacturer varies. You must pay attention to the number of connection endpoints of the vswitch ports during use.

If the number of MAC addresses exceeds the number of MAC addresses specified by the manufacturer, when the switch receives a network frame, only the MAC address of the target station does not exist in the MAC address table of the switch port, the frame is broadcast to each port of the vswitch.

2. Virtual Network Division

Virtual Network is an important function of the switch working principle. Generally, there are three ways to implement virtual network:

(1) Static port allocation

Static virtual networks are usually divided by network administrators using network management software or directly setting the port of a switch so that they can directly subordinate to a virtual network. These ports keep these properties until the Administrator resets them. Although this method is troublesome, it is safe and easy to configure and maintain.

(2) Dynamic Virtual Network

Supports Dynamic Virtual Network ports, which can be automatically determined by intelligent management software. The port is determined by using the MAC address, logical address, or protocol type of the Network Package. When a network node is connected to an access network.

The working principle port of the switch has not been assigned yet, so the switch dynamically transfers the port to a virtual network by reading the MAC address of the network node. In this way, once the network administrator is configured, the user's computer can flexibly change the switch port, without changing the user's Virtual Network's conformances. If an undefined MAC address appears in the network, you can send an alarm to the network administrator.

(3) Configure multiple virtual network ports

This configuration allows one user or one port to access multiple virtual networks at the same time. In this way, you can configure a network server as multiple business departments (each service is set as a virtual network) and access resources of multiple virtual networks at the same time, it also allows connections between multiple virtual networks to be completed through only one routing port.

But this will bring security risks. The specifications of the virtual network industry are being formulated, so the products of various companies are not interoperable. Cisco has developed the Inter-Switch Link (ISL) virtual network protocol, which supports virtual networks across Backbone Networks (ATM, FDDI, Fast Ethernet. However, the Protocol is accused of lack of security considerations. A large number of shared hubs are used in traditional computer networks, which can be achieved through flexible access to computer ports.

3. Application of High-speed LAN technology

Although the Fast Ethernet technology maintains good compatibility with the traditional large network in some aspects, 100BASE-TX, 100BASAE-T4, and 100BASE-FX impose great limitations on the transmission distance and cascade. A Mbps switch can break these limitations. At the same time, only the switch port can support duplex high-speed transmission.

Currently, CDDI/FDDI exchange technology has emerged. In addition, the port price of CDDI/FDDI has also declined, and it also has great advantages in terms of transmission distance and security, therefore, it is a good choice for large network backbone.

3COM's main switching products include Linkswitch series and LANplex series; BAY's main switching products include LattisSwitch2800, BAY stack workgroup, System3O00/5000 (some optional switching modules are provided ); cisco's main switch products include the Catalyst 1000/2000/3000/5000 Series.

The product forms of the three companies seem to have similarities, and the prices of the products are similar. In addition to the specific needs of the network environment in the design (the port combination is emphasized to be reasonable, it also needs to be considered as a whole, such as network management and network applications. With the development and maturity of ATM technology and the intensification of market competition, the price of frame switches will fall further, and it will become an important solution for working networking.