How switches work

Source: Internet
Author: User
Tags network function

I. Overview
In 1993, LAN switching equipment emerged. In 1994, the exchange network technology boom began in China. In fact,
Exchange Technology is a simplified, low-cost, high-performance and high-port intensive exchange product, reflecting the bridge technology
Complex exchange techniques in OSI reference model. The same as the bridge adapter
The MAC address is relatively simple in Decision-Making Information forwarding. This type of forwarding decision generally does not consider the deeper hidden content of the packet.
. 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 common
The forwarding performance between interconnected networks.
Exchange technology allows bandwidth adjustment between shared and dedicated LAN segments to reduce information flow between LAN segments.
Bottlenecks. 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
Small conflicting domains provide higher bandwidth for each workstation. Protocol transparency simplifies the configuration of vswitches in Software
The switch is directly installed in a multi-protocol network. The switch uses existing cables, reconnections, hubs, and work
The network card of the station does not need to be upgraded to a high-level hardware. The switch is transparent to the workstation, so the management cost is low and simple.
Added, moved, and changed network nodes.
Using a specially designed integrated circuit, the switch can forward information to all ports at the same speed in parallel to provide
The performance is much higher than that of traditional bridges. For example, theoretically, a single Ethernet port has 64 Octal numbers.
Data Package provides a transmission rate of 14880bps. This means that a machine with 12 ports and six parallel data streams is supported.
The "line rate" Ethernet switch must provide 89280bps
(X14880bps/information stream ). Dedicated integrated circuit technology enables switches
When multiple ports are used, the above performance is run, and 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 backboards of these hubs are usually divided into multiple
Each CIDR Block is a broadcast domain. The networks do not communicate with each other without a bridge or a route connection. To
After the main module is inserted, it is usually allocated to the network segment of a backplane. Port switching is used to forward the Ethernet module port to the back
The network segments of the Board are allocated and balanced. Based on the degree of support, port switching can also be subdivided:
· Module switching: migrate the entire module to the network segment.
· Port group switching: 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 exchange technology is based on
The first layer of OSI has the advantages of flexibility and load balancing. If configured properly, you can
A certain degree of customer errors, but did not change the characteristics of the shared transmission media, but failed to call it a real exchange.
2. Frame Switching
Frame switching is currently the most widely used LAN switching technology. It extracts
Mechanism for parallel transmission to reduce conflicting domains and obtain high bandwidth. Generally, the product implementation technologies of each company
However, network frames are generally processed in the following ways:
· Pass-through switching: Provides line rate processing capabilities. The switch reads only 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 and lacks intelligence and
Security, and cannot support port exchanges with different rates. Therefore, each vendor regards the latter technology
Important.
Some manufacturers even break down network frames and break down frames into fixed cells. This cell processing is very easy to use.
Hardware Implementation, fast processing, and advanced control functions such as the LET hub of MADGE)
For example, priority control.
3. Cell Exchange
The ATM technology represents the future direction of the development of network and communication technologies, and also solves many problems in the current network communication.
A good medicine, ATM uses a fixed length of 53 bytes of Cell Exchange. Because the length is fixed, it is easy to use hard
Component implementation. ATM uses dedicated non-differential connections for parallel operation. multiple nodes can be created simultaneously through one vswitch.
But does not affect the communication capability between each node. ATM also allows multiple virtual machines to be created on 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, LAN switches mainly refer
It is marked by factors such as port configuration, data exchange capability, and Packet Exchange speed. Therefore, when selecting a vswitch, pay attention
Next:
1) Number of switching ports;
2) Switch Port type;
3) system expansion capability;
4) main 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 advertised by manufacturers.
. In fact, this is a misunderstanding. The network used by workstations or servers connected to the access network is a large network, and it follows the CSMA/
CD media access rules. In the current customer/Server mode, multiple workstations access the server at the same time,
Therefore, it is very easy to form a server bottleneck. Some vendors have designed one or
Multiple high-speed ports such as Linkswitch1000 of 3COM
One or two Mbps ports can be configured to facilitate your connection to the server or high-speed backbone network. You can also access
Design multiple servers for Business Division) or append multiple NICs to eliminate the bottleneck. The switch can also be generated.
Tree Algorithm facilitates redundant connections with fault tolerance in your architecture.
2. 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. This type of LAN broadcast packet
The existence will greatly reduce the efficiency of the switch. In this case, you can use the virtual network function of the switch.
Supports virtual networks.
Each vswitch port supports a certain number of MAC addresses, so that the vswitch can "remember" The port.
When a group of sites are connected, the number of MAC addresses supported by different switch ports provided by the manufacturer is different.
Pay attention to the number of connection endpoints of the vswitch port. The switch receives
When a network frame is set, only the MAC address of the target station does not exist in the MAC address table of the vswitch port.
Each port sent to the vswitch in broadcast mode.
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 to direct
Connect to a virtual network. These ports keep these properties until the Administrator resets them. This method
Although it 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
Use the MAC address, logical address, or protocol type of the network package to determine the virtual network's subordination. When a network node is just connected
When the network is connected, the switch port is not allocated, so the switch dynamically changes the port by reading the MAC address of the Network Node
To a virtual network. In this way, once the network administrator is configured, the user's computer can flexibly change the switch end.
And does not change the virtual network of the user, and if there is an undefined MAC address in the network, you can
To send alerts to network administrators.
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 set up a network server
Configured as multiple business departments. Each business is configured as a virtual network.
Virtual Network Resources can also be connected between multiple virtual networks through only one routing port. However
Security risks. The specifications of the virtual network industry are being formulated. Therefore, the products of various companies cannot interact with each other.
Performance. Cisco developed the Inter-Switch
LinkISL) virtual network protocol, which supports cross-Backbone Network ATM, FDDI, Fast
Ethernet. However, the Protocol is accused of lack of security considerations. In traditional computer networks
Using a large number of shared hubs, you can also achieve good results 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 large limitations on the transmission distance and cascade. Transfer by Mbps
Changing hosts can break these limitations. At the same time, only the switch port can support duplex high-speed transmission.
Currently, CDDI/FDDI exchange technology has also emerged. In addition, the port prices of CDDI/FDDI are also declining.
It also has great advantages in terms of transmission distance and security. Therefore, it is a comparison of large network backbone.
Good choice.
3COM's main switching products include Linkswitch series and LANplex series; BAY's main switching products include Latt
IsSwitch2800, BAY
Stack workgroup, System3O00/5000 provides some optional switching modules); Cisco's main switching products
Product: 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. Besides the design
Considering the specific needs of the network environment, it is also necessary to emphasize the proper port combination.
Applications. With the development and maturity of ATM technology and the intensification of market competition, the price of frame switches will be further improved.
It will become an important solution for working networking.

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