Network Interconnection device lecture

Network Interconnection device lecture

Network Interconnection device Overview

When connecting a computer to a computer or workstation to a server, in addition to using the connection media, you also need some intermediary devices. What are the main intermediary devices? What role does it play? This is a concern in network design and implementation.

We divide commonly used connection devices into the following types:

I. network transmission media interconnection Device

When a network line is connected to a user node, the following situations may occur:

· T-type connector;

· Transceiver;

· Shielded or unshielded twisted pair connector rj -- 45;

· Rs232 interface (db -- 25 );

· Db -- 15 interface;

· Vb35 synchronization Interface;

· Network Interface Unit;

· Modem.

The t-type connector and the bnc connector are also fine coaxial cable connectors, which have a crucial impact on the availability of the network. The coaxial cable and the t-type connector depend on the bnc connector for connection. The bnc connector can be manually installed or tool-type installed. You can select the connector based on the actual situation and line availability.

The rj -- 45 unshielded twisted pair connector has eight pins. In the 10base-t standard, only four wires are used, that is, 1st pairs of twisted pair wires use 1st and 2nd pins, 2nd pairs of twisted pair wires use 3rd and 6th needles (3rd pairs and 4th pairs for backup ). For specific usage instructions, refer to the instructions provided by the manufacturer.

The db -- 25 (RS-232) interface is a common method of microcomputer and line interface.

Db -- 15 interface is used to connect the aui interface of the network interface card. Information can be sent to the transceiver through the transceiver cable and then enters the trunk media.

The vb35 synchronization interface is used to connect to a remote high-speed synchronization interface.

The terminal adapter is installed on two endpoints of the coaxial cable (coarse or fine) to prevent the cable from having no matching resistance or incorrect impedance. If there is no matching resistance or the impedance is incorrect, the signal waveform reflection may occur, resulting in a signal transmission error.

A modem is used to convert a computer's digital signal to a analog signal or vice versa for transmission over a telephone or Microwave Line. Modulation converts a digital signal to a analog signal. Demodulation converts a analog signal to a digital signal, which is generally connected to a computer through an RS-232 interface.

2. network physical layer interconnection devices

1. Repeater

As signals have attenuation and noise in the network transmission media, the useful data signals become weaker and weaker. Therefore, in order to ensure the integrity of the useful data and transmit it within a certain range, use a repeater to separate the received weak signal and regenerate and zoom in to keep it the same as the original data.

2. Hub

A hub is a special repeater. As a central node between network transmission media, it overcomes the defect of a single channel of media. The hub-centered advantage is that when a line or node in the network system fails, the normal operation of other nodes on the Internet will not be affected. Hubs can be divided into passive, active, and intelligent hubs.

The passive hub is only responsible for connecting multiple segments of media without any signal processing. Each media segment can be expanded to only half of the maximum valid distance.

An active hub is similar to a passive hub, but it has the ability to regenerate and enlarge transmission signals to expand the length of the media.

In addition to the functions of the active hub, the smart hub can also integrate some functions of the network into the hub, such as network management and network transmission line selection.

With the rapid development of hub technology, the Exchange Technology (line switching function added on the hub) and network segmentation methods have emerged, improving the transmission bandwidth.

With the development of computer technology, the hub is divided into three types: switch type, shared type and stackable shared type.

(1) Switch-type hub

A switched hub generates each signal again and filters each packet before sending, and only sends it to the destination address. The switched hub allows 10 Mbps and Mbps sites to be used in the same network segment.

(2) The shared hub provides a maximum bandwidth shared between sites at all connection points. For example, a 100 mbps shared hub connected to several workstations or servers provides a maximum bandwidth of mbps, which is shared with the sites connected to it. Shared hub does not filter or regenerate signals. All connected sites must work at the same speed (10 mbps or 100 mbps ). Therefore, shared hub is cheaper than switched hub.

(3) Stack-shared hub stack-shared hub is a type of shared hub. When they are connected together, it can be seen as a large hub in the network. When six eight-port hubs are connected together, they can be regarded as one hub with 48 ports.

Iii. data link layer interconnection devices

1. Bridge

A bridge is a bridge between a LAN and another LAN. A bridge is a device at the network layer. It is used to expand the network and communication means, forward data signals in various transmission media, and expand the network distance, at the same time, it selectively sends an address signal from one transmission medium to another, and can effectively restrict unnecessary communication between the two media systems. Bridges can be divided into local bridges and remote bridges. A local bridge is a bridge that connects networks within the allowed length range of the transmission media. A remote bridge is a remote bridge that is used when the distance from the network exceeds the normal range, a lan interconnected through a remote bridge will become a man or WAN. If a remote bridge is used, the remote bridge must appear in pairs.

In the local connection of the network, the bridge can use the internal and external bridges. The inner bridge is part of the file service. It is managed by the Network * running on the file server through the LAN connected by different network cards on the file server. The Outer Bridge is installed on a workstation to connect two similar or different networks. The Outer Bridge does not run on the network file server, but runs on an independent workstation. The outer bridge can be dedicated or non-dedicated. A workstation that acts as a dedicated bridge cannot be used as a normal workstation, but can only build a bridge between two networks. A workstation other than a dedicated bridge can be either a bridge or a workstation.

2. Switch

Network exchange technology is a structured network solution developed in recent years. It is a new network application form that emerged from the development of computer networks to the high-speed transmission phase. It is not a new network technology, but an existing network technology that improves performance through switching devices. Due to the rapid development of the switch market, a wide range of products, and more powerful functions, we use enterprise-level, department-level, working-level, and switch-to-desktop classification.

4. Network Layer interconnection devices

A router is used to connect multiple logically separated networks. A logical network is a separate network or a subnet. When data is transmitted from one subnet to another, it can be done through a router. Therefore, a vro can determine the network address and select the path. It can establish flexible connections in Multi-network interconnection environments and connect subnets using different data groups and media access methods. A router is an interconnected device at the network application layer. It only receives information from the source station or other routers. It does not care about the hardware devices used by each subnet, however, it is required to run software consistent with the network layer protocol. Routers are divided into local routers and remote routers. Local routers are used to connect network transmission media, such as optical fiber cables, coaxial cables, and twisted pair wires; A remote router is a device that is used to connect to a remote transmission medium and requires a corresponding device. For example, a telephone line must be equipped with a modem and a wireless receiver and a transmitter.

5. Application Layer interconnection devices

In a computer network, when connecting different types of networks with Large Protocol differences, You must select a gateway device. The function of the gateway is reflected in the top layer of the osi model. It converts the protocol and groups the data to facilitate communication between two different types of network systems. Protocol conversion is complicated. In general, gateways only perform one-to-one conversion, or convert a few specific application protocols. It is difficult for gateways to implement universal protocol conversion. The application protocols used for gateway conversion include email, file transfer, and Remote Workstation logon.

Gateways and multi-protocol routers (or communication servers for special purposes) can be combined to connect multiple different systems.

Like a bridge, a gateway can be either local or remote.

Currently, the gateway has become a common tool for every user on the network to access large hosts.

Repeater and hub

I. Repeater

A repeater (rp repeater) is a device that connects to a network line and is often used for Bidirectional Forwarding of physical signals between two network nodes. As the simplest network interconnection device, relay is mainly responsible for transmitting information by bit on the physical layer of two nodes to complete signal replication, adjustment, and amplification, to extend the length of the network. It is shown in position 1 in the osi reference model.

Due to the loss, the signal power transmitted on the line will gradually decrease, and the signal distortion will occur when the signal is reduced to a certain extent, resulting in receiving errors. Repeater is designed to solve this problem. It completes the connection of the physical line and scales up the attenuation signal to keep it the same as the original data.

Generally, the two ends of the repeater connect the same media, but some relay can also transfer different media. Theoretically, the use of relay is infinite, and the network can be extended infinitely. In fact, this is not possible, because network standards have specific provisions on the signal delay range, relay can only be effective within this range of work, otherwise it will cause a network failure. In the Ethernet network standard, only five network segments are allowed on an Ethernet network, and a maximum of four reconnections are allowed. In addition, only three network segments can be mounted to computer terminals.

2. Hub

A hub is a form of relay. The difference is that a hub can provide multi-port services, also known as multi-port relay. Location 2 of the hub in osi/rm.

Hub products develop rapidly. lan hubs are generally divided into five different types, which will have a direct impact on the development of lan switch technology.

1. Single-relay CIDR Block Hub

On the hardware platform, the first type of hub is a simple relay lan CIDR block. The best example is a stacked Ethernet Hub or a mau ). Some vendors try to draw a line between manageable and unmanageable hubs for hardware classification. The core features of the network hardware are ignored here, that is, what functions it implements, rather than how to configure it easily.

2. Multi-CIDR Block Hub

A multi-CIDR Block hub is derived directly from the first type of hub and uses a hub backplane that carries multiple relay network segments. A multi-segment hub is usually a chassis system with multiple interface card slots. However, some non-modular stacked hubs now support multiple relay network segments. The main technical advantage of a Multi-CIDR Block hub is that users can be distributed across multiple relay CIDR blocks to reduce the information traffic load of each CIDR block, information traffic between CIDR blocks generally requires independent bridges or routers.

3. Port exchange Hub

A port exchange hub automates the connection process between user ports and multiple backplane network segments based on a multi-Network-segment hub and is implemented by adding a port exchange matrix (psm. The SMS provides an automatic tool to connect any external user port to any relay network segment on the hub backplane. The key to this technology is "matrix". A matrix switch is a cable switch which cannot be implemented automatically and requires user intervention. It cannot replace bridges or routers and does not provide connectivity between different lan network segments. Its main advantage is to automate the movement, addition, and modification.

4. Network Interconnection Hub

Port-switched hubs focus on port switching, while network hubs provide some types of Integrated connections between multiple network segments on the backplane. This can be done through an integrated bridge, router, or lan switch. Currently, these hubs are usually in the form of chassis.

5. Exchange Hub

At present, the boundaries between the hub and the switch have become blurred. The exchange hub has a core exchange backplane that uses a pure exchange system to replace the traditional shared media relay network segment. Such products are available and hybrid (relay/switch) hubs are likely to control the market in the next few years. It should be noted that there is almost no difference between the characteristics of the hub and the switch.

A bridge established in a lan

A bridge, also known as a bridge, is a storage and forwarding device that connects two local networks. It can be used to connect network systems with the same or similar architecture. Generally, the connected network system has the same Logical Link Control Procedure (llc), but the media access control protocol (mac) can be different.

A bridge is a connection device on the data link layer. He accurately says it works on the mac sublayer. The bridge transmits information through indirect frames at the data link layer (ddl) of two local networks.

The bridge is designed to store and forward data in various LAN networks. It is transparent to End Node users. When the end node transmits packets through the bridge, it does not know the existence of the bridge.

A bridge can connect the same or different LAN networks to form an extended LAN.

I. Working Principle of Bridges

To illustrate the working principle of the bridge, we will describe it in the context of fddi.

Fddi is an open network that allows various network devices to exchange data. The two local networks connected by a bridge can be based on the same standard or two different types of standards. When the bridge receives a data frame, it first sends it to the data link layer for error verification, then sends it to the physical layer, and then transmits it to another subnet through the physical layer transmission mechanism. Before Frame Forwarding, the bridge does not modify the format and content of frames. Generally, bridges have enough buffers. Some bridges also have certain routing functions to reduce information traffic on the Internet by filtering unnecessary transmission in the network.

For example, when the fddi site has a message to be sent to the ieee 802.3 csma/cd network on the internet, you need to complete the following work:

· The site first transmits the message to the llc layer and adds the llc header.

· Send the packet to the mac layer and add the fddi header. The maximum length of an fddi packet is 4500 bytes. packets larger than this value can be sent in groups.

· The maximum length of an fddi packet is 4500 bytes. If the value is greater than this value, it is sent to the fddi-ieee 802.3 Ethernet bridge.

· Remove the fddi header from the mac layer on the bridge and send it to the llc layer for processing.

· After reframing and calculating the verification value, the ieee 802.3 data frame format is formed and added to the front.

· Transmit frames to the ieee 802.3 Ethernet site through transmission media.

Because the fddi transmission rate (100 mbps) does not match the IEEE 802.3 Ethernet transmission rate (10 mbps), congestion and timeout problems exist on the bridge, and re-transmission may occur. If multiple resends fail, the system will stop sending the message and notify the target site that the network may be faulty.

Ii. Functions of Bridges

An fddi bridge should include the following basic functions:

1. Source Address tracking

The bridge has a certain path selection function. After receiving a frame at any time, it must determine its correct transmission path and send the frame to the corresponding destination site. The net bridge records the source address in the frame to its forwarding database (or address query table). The forwarding database is stored in the memory of the Net Bridge, this includes the addresses of all connected sites that the bridge can see. This address database is exclusive to the Internet. It specifies the direction of the received frame, or only indicates which side of the bridge receives the frame. The bridge that can automatically establish such a database is called an adaptive bridge.

In an extended network, all bridges should adopt an adaptive method to obtain the addresses of all sites associated with it. Bridges constantly update their forwarding databases during their work to make them more complete. Bridges provided by some vendors allow users to edit address Lookup tables, which facilitates network management.

2. Frame Forwarding and filtering

The bridge acts as a frame forwarding between two interconnected local networks. It allows sites on each lan to communicate with other sites, and looks like a network extension.

To effectively forward data frames, the bridge provides storage and forwarding functions. It automatically stores received frames and completes addressing through the address query table; then, it is forwarded to the target site on the other side of the source address, and the frames with the same source address side are deleted from the storage area.

Filtering is a process that prevents frames from passing through the bridge. There are three basic types:

(1) Destination Address filtering when a bridge receives a frame from the network, first determine its source address and destination address. If the source address and destination address are in the same LAN, simply discard it, otherwise it will be forwarded to another LAN, which is called destination address filtering.

(2) source address filtering the so-called source address filtering means to reject the forwarding of a specific address frame as needed. This specific address cannot be obtained from the address lookup table, however, it can be provided by the network management module. In fact, not all bridges filter source addresses.

(3) protocol filtering currently, some bridges can also provide protocol filtering functions, which are similar to source address filtering. Network Management instructs bridges to filter specified protocol frames. In this case, the bridge decides whether to forward or filter the frame based on the protocol information of the frame. Such filtering is usually only used to control the traffic, isolate the system, and provide security protection for the network system.

3. Deduction of Spanning Tree

The spanning tree (spanning tree) is an industrial standard algorithm based on ieee 802.1d. It can be used to prevent loop generation on the Internet, because the loop will cause network faults. The spanning tree has two main functions:

· There is only one logical path between any two LAN networks;

· Connect all networks to a single extended LAN with no repeated paths between two or more bridges.

The logical topology of the extended lan must be non-loop, and all connected sites have a unique path. In the extended network system, the bridge exchanges information through a special frame named greeting frame, which is used to determine who forwards and who is idle. It is determined that the bridge to perform the forwarding should also be responsible for Frame Forwarding, while the idle bridge can be used as a backup.

4. Protocol Conversion

The early fddi bridge structure is usually a dedicated encapsulation structure, because the early fddi is only connected to the 802.3 or 802.5 subnet, and does not need to communicate with nodes in other LAN. However, in a large extended LAN, many systems work together. This dedicated encapsulated bridge cannot provide the capability to work with each other. To this end, a new conversion technology is adopted. According to the bridge standards with other networks, a conversion bridge is formed to establish a standard frame that can adapt to lan interconnection.

(1) encapsulation bridge)

Using some dedicated devices and technologies, fddi is used as a transmission pipeline, which requires the use of the same model of bridges on the Internet, which undoubtedly affects the performance of network interaction.

Taking the fddi-ethernet bridge as an example, the fddi encapsulation Bridge uses the dedicated protocol technology to encapsulate an ethernet frame with the fddi header and End message, and then forwards the frame to the fddi network, the destination address is also hidden in the encapsulated frame. The encapsulation bridge sends the fddi frame to another encapsulation bridge. The encapsulation Bridge uses the unpacking technology corresponding to the encapsulation technology to remove the encapsulation. Because the destination address is encapsulated, frames can only be sent in the form of broadcast frames, which will undoubtedly reduce the network bandwidth usage. If the Internet is large and contains many bridges and local networks, the number of broadcast frames will also increase, which will inevitably cause unnecessary congestion.

Encapsulation bridges cannot send data through the conversion bridge. Only the same encapsulation bridge provided by the same supplier can work together, nor can they transmit data through the encapsulation bridge provided by other suppliers, unless the encapsulated bridge provided by other vendors also uses this dedicated protocol.

(2) The translation bridge overcomes the disadvantages of the encapsulation bridge, converts the frames to be transmitted into the frame format of the destination network, and then transmits them online.

Take the fddi-ethernet bridge as an example. To use a high-performance server connected to fddi for a large network workstation, you must first convert the ethernet frame format to the fddi frame format, then it is transmitted to the target server through fddi. In this case, the server receives a frame in fddi format, so it can be used without any changes. It can be seen that the conversion bridge is common. Any converted bridge can communicate with other bridges.

5. Frame splitting and restructuring

The complexity of Internet connection depends on the difference in the packets, frames, and protocols of the Internet. Different types of networks have different parameters, including the error Verification Algorithm and the maximum packet grouping, and different lifecycles. For example, in the fddi network, the maximum frame length is 4500 bytes, and in the ieee 802.3, the maximum frame length is 1518 bytes. In this way, when fddi forwards data frames to ethernet, the bridge must divide the 4500-byte frame of fddi into several 1518-byte ieee 802.3 protocol ethernet frames, and then forward the frames to the Internet, this is frame splitting technology. Some Common Communication Protocols define similar methods for controlling frame size differences (called packet splitting ). On the contrary, when ethernet forwards data frames to fddi, only 1518-byte ethernet frames must be combined into fddi frames and transmitted in fddi format. This is frame restructuring.

For protocols and applications that use long message formats, frame separation and restructuring are very important. If the fddi bridge does not have the frame splitting and restructuring functions, it cannot be achieved through the bridge interconnection. However, in the protocol conversion process, frame splitting and restructuring must be completed quickly, otherwise the performance of the bridge will be reduced.

6. Manage Bridges

Another important function of the bridge is to monitor the status of the extended network. The purpose is to better adjust the topology logic structure. Some bridges can also collect statistics on the forwarding and loss of frames, for system maintenance. Bridge Management can also indirectly monitor and modify the forwarding address database, allowing the network management module to determine the location of the network user site, in order to manage a larger network expansion. In addition, the deduction process of the network topology can be well coordinated by adjusting the deduction parameters of the Spanning Tree.

Iii. Types of Bridges

1. Inner Bridge

The Inner Bridge is a LAN connected by different NICs in the file server.

2. Outer Bridge

The Outer Bridge is different from the internal bridge. The Outer Bridge is installed on the workstation. It can be dedicated or non-dedicated to connect two similar Local Area Network outer bridges. A private outer bridge cannot be used as a workstation. It can only be used to establish connections between two networks and manage communications between networks. Non-dedicated outer bridges act as bridges and can be used as workstations.

3. Remote Bridge

A Remote Bridge is a device that connects to a remote network. Generally, a remote bridge uses a modem and a transmission medium, such as a telephone line to connect two local networks.

How switches work

I. Overview

In 1993, LAN switching equipment emerged. In 1994, the exchange network technology boom began in China. In fact, the exchange technology is a simplified, low-cost, high-performance and high-port intensive exchange product, reflecting the complex exchange technology of the bridge technology in the osi reference model layer 2. Like the bridge adapter, the switch simply decides to forward information based on the mac address in each package. This type of forwarding decision generally does not consider the deeper information hidden in the package. The difference with the bridge adapter is that the forwarding latency of the switch is very small. * The performance is close to that of a single LAN, far exceeding the forwarding performance between common Bridging networks.

The exchange technology allows the shared 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.

Similar to traditional bridges, vswitches provide many network interconnection functions. Vswitches can economically divide networks into small conflicting domains to provide higher bandwidth for each workstation. How does protocol transparency make the vswitch easy to configure in software? Benzene shadow Cang Ba Zheng published a school call for Meng Zhongxing machinery Xiao Long Xiao Tang Jing Li Xiao Jing Xiao bu ding call in exchange for complaints, the model of the moles, the Earth, the moles, the stunned brain, the printing, the poor, the poor? .

The dedicated Integrated Circuit enables the switch to forward information in parallel at all ports at the line rate, providing a much higher * performance than the traditional bridge. For example, theoretically, a single Ethernet port can provide a transmission rate of 14880bps for data packets containing 64 octal packets. This means that a "line rate" Ethernet switch with 12 ports that support six parallel data streams must provide an overall throughput of BPS (6-channel information flow X14880bps/channel information flow ). The dedicated integrated circuit technology enables the switch to run with more ports. The port cost is lower than that of the traditional bridge.

Ii. Three exchange technologies

1. Port Switching

Port switching technology first appeared in a slot hub. The backplane of these hubs is usually divided into multiple Ethernet segments (each segment is a broadcast domain) without a bridge or route connection, networks do not communicate with each other. After the master module is inserted, it is usually allocated to the network segment of a backplane. Port switching is used to allocate and balance the Ethernet module ports among multiple network segments of the backplane. Based on the degree of support, port switching can also be subdivided:

· Module switching: migrate the entire module to the 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 advantages of flexibility and load balancing capabilities. If properly configured, the customer can still make a certain degree of errors, but it does not change the characteristics of the shared transmission media, rather than being called a real exchange.

2. Frame Switching

Frame switching is currently the most widely used LAN switching technology. It provides a parallel transmission mechanism to reduce conflicting domains and obtain high bandwidth by performing differential segments on Traditional transmission media. Generally, the implementation technologies of each company's products are different, but there are generally the following processing methods for network frames:

· Pass-through switching: Provides line rate processing capabilities. The switch only reads the first 14 bytes of the network frame and then transfers the network frame to the corresponding port.

· Storage 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.

Some manufacturers even break down network frames and break down frames into fixed cells. This cell processing is easy to implement by hardware, and the processing speed is fast, at the same time, it can complete advanced control functions (such as the let hub of madge) such as priority control.

3. Cell Exchange

The atm technology represents the future direction of the development of network and communication technologies. It is also an outstanding solution to the numerous difficulties in network communication. The Home Insurance tm uses a fixed length of 53 bytes of Cell Exchange. Because the length is fixed, it is easy to implement with hardware. Atm uses dedicated non-differential connections and runs in parallel. multiple nodes can be established through a switch at the same time, but the communication capability between each node is not affected. Atm also allows multiple virtual links at the source node, target node, and node to ensure sufficient bandwidth and fault tolerance. The statistical time-division circuit is used in atm, which can greatly improve the channel utilization. The bandwidth of an atm can reach 25 m, 155 m, m, or even several gb.

Iii. LAN switch types and selection

LAN switches can be divided:

· Large network switches;

· A wildcard ring switch;

· Fddi switch;

· Atm switch;

· Fast Ethernet switch.

Divided by the switch application field, it can be divided:

· Desktop switches;

· Workgroup switches;

· Trunk switch;

· Enterprise switches;

· Segmented switch;

· Port switch;

· Network switches.

LAN switches are the core devices that make up the network system. For users, the main indicators of LAN switches are port configuration, data exchange capability, Packet Exchange speed, and other factors. Note the following when selecting a vswitch:

(1) Number of switch ports;

(2) Switch Port type;

(3) system expansion capability;

(4) trunk line connection means;

(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.

4. Several notable problems in Switch Applications

1. bottlenecks in vswitch Networks

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 the linkswitch1000 of 3com) to facilitate the user 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.

2. Broadcast frames in the Network

Currently, netware and windows nt are widely used Network * 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.

3. Virtual Network Division

A virtual network is an important function of a vswitch. Generally, there are three ways to implement a 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 just connects to the access network, the switch port is not allocated, so the switch dynamically switches the port into 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. Therefore, the products of various companies cannot interact with each other. 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.

4. 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.