What is a lan switch. What is a switch and why are such devices needed? High-end switch architecture

If previously the network cable through which data was transferred was simply connected directly to the computer, now the situation has changed. In one residential apartment, office or large company, there is often a need to create a computer network.

For this purpose, devices that are included in the “computer equipment” category are used. Such devices also include a switch that allows . So what is a switch, and how to use it to build a computer network?

What are switch devices used for?

Literally translated from English language, the computer term "switch" refers to a device that is used to create local network through the connection of several computers. A synonym for the word switch is switch or switch.

A switch is a kind of bridge with many ports through which packet data is transmitted to specific recipients. The switch helps optimize the operation of the network, reduces the load on it, increases the level of security, and records individual MAC addresses, which allows you to quickly and efficiently transfer data.

Such switches were able to displace hubs, which were previously used to build computer networks. A switch is a smart device that can process received information about connected devices and then redirect the data to a specific address. As a result, network performance increases several times and Internet speeds up.

Types of equipment

Switch devices are divided into different types according to the following criteria:

• Type of ports.
• Number of ports.
• Port speeds are 10 Mbit/s, 100 Mbit/s and 1000 Sbit/s.
• Managed and unmanaged devices.
• Manufacturers.
• Functions.
• Technical specifications.

By the number of ports, switch switches are divided into:

• 8-port.
• 16-port.
• 24-port.
• 48-port.

For home and small offices, a switch with 8 or 16 ports that operate at a speed of 100 Mbit/second is suitable.

For large enterprises, companies and firms, ports with an operating speed of 1000 Mbit per second are needed. Such devices are needed to connect servers and large communications equipment.

Unmanaged switches are the simplest of equipment. Complex switches are managed at the network or third layer of the OSI model - Layer 3 Switch.

Management is also carried out through methods such as:

• Web interface.
• Command line interface.
• SNMP and RMON protocols.

Complex or managed switches allow VLAN, QoS, mirroring, and aggregation features. Also, such switches are combined into one device called a stack. It is designed to increase the number of ports. Other ports are used for stacking.

What do providers use?




When creating a computer network, provider companies create one of its levels:

• Access level.
• Aggregation level.
• Kernel level.

Levels are needed to make it easier to handle the network: scale, configure, introduce redundancy, design the network.

At the access level of the switch device, a connection must be made end users to a 100 Mbit/s port. Other requirements for the device include:

• Connection via SFP to an aggregation level switch, where information is transferred at a speed of 1 gigabyte per second.
• Support VLAN, acl, port security.
• Support for security features.

According to this scheme, three layers of the network are created from the Internet provider. First, the network is formed at the level of a residential building (multi-story, private).

Then the network is “scattered” throughout the neighborhood, when several residential buildings, offices, and companies are connected to the network. At the last stage, a core-level network is created, when entire neighborhoods are connected to the network.

Internet providers form a network using Ethernet technology, which allows subscribers to connect to the network.

How does the switch work?


The switch memory contains a MAC table in which all MAC addresses are collected. The switch receives them in the switch port node. When the switch is connected, the table is not yet filled, so the equipment operates in training mode. The data arrives at other ports of the switch, the switch analyzes the information and determines the MAC addresses of the computer from which the data was transferred. At the last stage, the address is entered into the MAC table.

Thus, when a data packet that is intended only for one PC arrives at one or another equipment port, the information is transmitted addressed to the specified port. When the MAC address has not yet been determined, the information is transmitted to the remaining interfaces. Traffic localization occurs during the operation of the switch device, when the MAC table is filled with the necessary addresses.

Features of setting device parameters

Making appropriate changes to the switch device parameters is the same for each model. Setting up the equipment requires step-by-step actions:

1. Create two VLAN ports - for clients and for managing switches. VLANs must be designated in the settings as switch ports.
2. Configure port security, prohibiting receiving more than one MAC address per port. This will avoid transmitting information to another port. Sometimes a brodux domain fusion may occur home network with the provider's domain.
3. Disable STP on the client port to prevent other users from polluting the provider's network with various BPDU packets.
4. Configure the loopback detection parameter. This will allow you to reject incorrect, defective network cards, and not interfere with the work of users connected to the port.
5. Create and configure an acl parameter to prohibit non-PPPoE packets from entering the user's network. To do this, in the settings you need to block unnecessary protocols such as DCHP, ARP, IP. Such protocols are designed to allow users to communicate directly, bypassing PPPoE protocols.
6. Create an acl that denies PPPoE RADO packets coming from client ports.
7. Enable Storm Control, which will allow you to fight multicast and broadcast floods. This parameter should block non-PPPoE traffic.

If something goes wrong, then it's worth checking PPPoE, which can be attacked by viruses or fake data packets. Due to inexperience and ignorance, users may incorrectly configure the last parameter, and then they need to contact their Internet service provider for help.

How to connect the switch?

Creating a local network of computers or laptops requires the use network switch– switch. Before setting up the equipment and creating the desired network configuration, the process of physically deploying the network occurs. This means that a connection is created between the switch and the computer. To do this, you should use a network cable.

Connections between network nodes are made using a patch cord - a special type of network communication cable made on the basis of twisted pair. Network cable It is recommended to purchase from a specialized store so that the connection process goes smoothly.

You can configure the switch in two ways:

1. Through the console port, which is intended for making initial switch settings.
2. Via a universal Ethernet port.

The choice of connection method depends on the equipment interface. Connecting through the console port does not consume any switch bandwidth. This is one of the advantages of this connection method.

You need to launch the VT 100 terminal emulator, then select connection parameters in accordance with the designations in the documentation. When the connection occurs, the user or employee of the Internet company enters a login and password.

To connect via the Ethernet port, you will need an IP address, which is indicated in the documents for the device or requested from your provider.

When the settings are made and the switch is created using computer network, users from their PCs or laptops should be able to access the Internet without any problems.

When choosing a device to create a network, you need to consider how many computers will be connected to it, what the speed of the ports is, and how they work. Modern providers use to connect Ethernet technology, allowing you to get a high-speed network using a single cable.

The choice of router to use is determined by the Ethernet interfaces that match the switch technology at the center of the LAN. It is important to note that routers offer many LAN services and features.

Each LAN has a router, which is used as a gateway to connect the LAN to other networks. A LAN has one or more hubs or switches to connect end devices to the LAN.

Routers are the main devices used to connect networks. Each port on the router connects to a different network and routes packets between networks. Routers can break up broadcast and collision domains.

Routers are also used to connect networks that use different technologies. They can have both LAN and WAN interfaces.

The LAN interfaces of routers allow them to connect to LAN media. Typically these are UTP cable connections, but modules can be added to allow fiber optics. Depending on the series or model of routers, they may have several types of interfaces for WAN and LAN cable connections.

Intranet devices

To create a LAN, we must select appropriate devices to connect the end nodes to the network. The two most common devices used are hubs and switches.

Hub

The hub receives the signal, regenerates it and sends it to all ports. The use of hubs creates a logical bus. This means that the LAN uses the media in multi-access mode. Ports take the approach sharing bandwidth, which often results in reduced LAN performance due to collisions and recovery. Although multiple hubs can be connected, there will still be a single collision domain.

Hubs are less expensive than switches. A hub is usually chosen as an intermediary device for a very small LAN that has low bandwidth requirements, or where finances are limited.

Switch

The switch receives the frame and regenerates each bit of the frame to the corresponding destination port. This device is used to segment the network into multiple collision domains. Unlike a hub, a switch reduces the number of collisions on the LAN. Each port on the switch creates a separate collision domain. This creates a logical point-to-point topology for the device on each port. In addition, the switch provides dedicated bandwidth on each port, which can improve LAN performance. A LAN switch can also be used to connect network segments at different speeds.

In general, switches are chosen to connect devices to the LAN. Although a switch is more expensive than a hub, its improved performance and reliability make it cost-effective.

There is a whole range of switches available with a variety of features that allow you to connect many computers in a typical enterprise LAN setup.

This chapter introduces technologies operating in devices that are imprecisely referred to as bridges And switches. Topics summarized here include general principles of channel devices, local and remote bridges, ATM and LAN switching. The subsequent chapters of Part 4, “Bridges and Switches,” of this book are devoted to the specifics of these technologies in more detail.

What are Bridges and Switches?

Bridges and switches are data communication devices that operate fundamentally at Layer 2 reference model OSI. As such, they generally refer to devices link layer.

The bridges became commercially available in the early 1980s. At the time of their introduction, bridges connected and allowed packets to be sent between homogeneous networks. In more recent times, building bridges between various networks was also defined and standardized.

Several types of bridges have become important as internetworking devices. Transparent bridges found primarily in Ethernet environments, whereas bridges with pre-routing (source-route bridge) appear primarily in the Token Ring environment. Translational Bridge provide translation between formats and transit principles various types media (usually Token Ring and Ethernet). Finally, transparent bridges with pre-routing (source-route transparent bridge) combine transparent and pre-routing bridging algorithms to enable communications in mixed Ethernet/Token Ring environments.

Today, switching technology has emerged as an evolutionary successor to bridge-based internetworking solutions. The use of switches now dominates applications where bridges were used in early networking designs. Superior throughput performance, higher port density, lower cost per port, and greater flexibility have contributed to the emergence of switches as a replacement technology for bridging and a complement to routing technology.

Overview of Link Layer Devices

Although bridges and switches share most of the same characteristics, several features distinguish these technologies. Switches are much faster because they switch in hardware, whereas bridges switch in software, and can also connect local networks with unequal bandwidth. For example, 10- and 100-Mbit Ethernet local networks can be connected using a switch. Switches also support higher port densities than bridges. Some switches support cut-through switching, which reduces network latency and latency, while bridges support only store-and-forward switching. Finally, switches reduce collisions on network segments by providing dedicated bandwidth to each network segment.

Types of bridges

03/18/1997 Dmitry Ganzha

Switches occupy a central place in modern local area networks. TYPES OF SWITCHING SWITCHING HUBS METHODS OF PACKET PROCESSING RISC AND ASIC ARCHITECTURE OF HIGH-CLASS SWITCHES BUILDING VIRTUAL NETWORKS THIRD LEVEL SWITCHING CONCLUSION Switching is one of the most popular modern technologies.

Switches occupy a central place in modern local area networks.

Switching is one of the most popular modern technologies. Switches are displacing bridges and routers to the periphery of local networks, leaving behind them the role of organizing communication through global network. This popularity of switches is primarily due to the fact that they allow, through microsegmentation, to increase network performance compared to shared networks with the same nominal bandwidth. In addition to dividing the network into small segments, switches make it possible to organize connected devices into logical networks and easily regroup them when necessary; in other words, they allow you to create virtual networks.

What is a switch? According to the IDC definition, “a switch is a device designed in the form of a hub and acting as a high-speed multiport bridge; the built-in switching mechanism allows segmentation of the local network and allocation of bandwidth to end stations in the network” (see M. Kulgin’s article “Build a network, plant a tree..." in the February issue LAN). However, this definition applies primarily to frame switches.

TYPES OF SWITCHING

Switching usually refers to four different technologies - configuration switching, frame switching, cell switching, and frame-to-cell conversion.

Configuration switching is also known as port switching, where a specific port on a smart hub module is assigned to one of the internal Ethernet segments (or Token Ring). This assignment is made remotely through software network management when users and resources join or move on the network. Unlike other switching technologies, this method does not improve the performance of the shared LAN.

Frame switching, or local network switching, uses standard formats Ethernet (or Token Ring) frames. Each frame is processed by the nearest switch and transmitted further across the network directly to the recipient. As a result, the network turns into a set of parallel high-speed direct channels. We will look at how frame switching is carried out inside a switch below using the example of a switching hub.

Cell switching is used in ATM. The use of small fixed-length cells makes it possible to create low-cost, high-speed switching structures at the hardware level. Both frame switches and mesh switches can support multiple independent workgroups regardless of their physical connection (see the section "Building virtual networks").

The conversion between frames and cells allows, for example, a station with an Ethernet card to communicate directly with devices on an ATM network. This technology is used to emulate a local network.

IN this lesson We will be primarily interested in frame switching.

SWITCHING HUBS

The first switching hub, called EtherSwictch, was introduced by Kalpana. This hub made it possible to reduce network contention by reducing the number of nodes in a logical segment using microsegmentation technology. Essentially, the number of stations in one segment was reduced to two: the station initiating the request and the station responding to the request. No other station sees the information transmitted between them. Packets are transmitted as if through a bridge, but without the delay inherent in a bridge.

In a switched Ethernet network, each member of a group of multiple users can simultaneously be guaranteed throughput 10 Mbit/s. The best way to understand how such a hub works is to use an analogy with a regular old telephone switch, in which the participants in the dialogue are connected by a coaxial cable. When a subscriber called “eternal” 07 and asked to be connected to such and such a number, the operator first of all checked whether the line was available; if so, he connected the participants directly using a piece of cable. No one else (with the exception of the intelligence services, of course) could hear their conversation. After the call ended, the operator disconnected the cable from both ports and waited for the next call.

Switching hubs operate in a similar way (see Figure 1): they forward packets from an input port to an output port through the switch fabric. When a packet arrives at an input port, the switch reads its MAC address (i.e., layer 2 address) and it is immediately forwarded to the port associated with that address. If the port is busy, the packet is placed in a queue. Essentially, a queue is a buffer on an input port where packets wait for the desired port to become free. However, the buffering methods are slightly different.

Figure 1.
Switching hubs function similarly to older telephone switches: they connect an input port directly to an output port through a switch fabric.

PACKET PROCESSING METHODS

In end-to-end switching (also called in-flight switching and bufferless switching), the switch reads only the address of the incoming packet. The packet is transmitted further regardless of the absence or presence of errors in it. This can significantly reduce packet processing time, since only the first few bytes are read. Therefore, it is up to the receiving party to identify defective packets and request their retransmission. However, modern cable systems are reliable enough that the need for retransmission on many networks is minimal. However, no one is immune to errors in the event of a damaged cable, faulty network card, or interference from an external electromagnetic source.

When switching with intermediate buffering, the switch, receiving a packet, does not transmit it further until it reads it completely, or at least reads all the information it needs. It not only determines the recipient's address, but also checks the checksum, i.e. it can cut off defective packets. This allows you to isolate the error-producing segment. Thus, buffer-and-forward switching emphasizes reliability rather than speed.

Apart from the above two, some switches use a hybrid method. Under normal conditions, they perform end-to-end switching, but they monitor the number of errors by checking checksums. If the number of errors reaches a specified threshold, they enter switching mode with forward buffering. When the number of errors decreases to an acceptable level, they return to end-to-end switching mode. This type of switching is called threshold or adaptive switching.

RISC AND ASIC

Often, buffer-forward switches are implemented using standard RISC processors. One advantage of this approach is that it is relatively inexpensive compared to ASIC switches, but it is not very good for specialized applications. Switching in such devices is carried out using software, therefore their functionality can be changed by upgrading the installed software. Their disadvantage is that they are slower than ASIC-based switches.

Switches with ASIC integrated circuits are designed to perform specialized tasks: all their functionality is “hardwired” into the hardware. There is also a drawback to this approach: when modernization is necessary, the manufacturer is forced to rework the circuit. ASICs typically provide end-to-end switching. The switch fabric ASIC creates dedicated physical paths between an input and output port, as shown in .

ARCHITECTURE OF HIGH-CLASS SWITCHES

High-end switches are typically modular in design and can perform both packet and cell switching. Modules of such a switch carry out switching between networks different types, including Ethernet, Fast Ethernet, Token Ring, FDDI and ATM. In this case, the main switching mechanism in such devices is the ATM switching structure. We will look at the architecture of such devices using the Bay Networks Centillion 100 as an example.

Switching is accomplished using the following three hardware components (see Figure 2):

(1x1)

Figure 2.
In high-end switches, cell switching is increasingly used due to its high speed and ease of migration to ATM.

Each switch module has I/O ports, buffer memory, and a CellManager ASIC. In addition, each LAN module also has a RISC processor to perform frame switching between local ports and a packet assembler/disassembler to convert frames and cells into each other. All modules can independently switch between their ports, so that only traffic destined for other modules is sent through the backplane.

Each module maintains its own table of addresses, and the main control processor combines them into one common table, so that an individual module can see the network as a whole. If, for example, an Ethernet module receives a packet, it determines who the packet is addressed to. If the address is in the local address table, then the RISC processor switches the packet between local ports. If the destination is on another module, then the assembler/disassembler converts the packet into cells. The CellManager specifies a destination mask to identify the module(s) and port(s) to which the cells payload is destined. Any module whose board mask bit is specified in the destination mask copies the cell to local memory and transmits the data to the corresponding output port in accordance with the specified port mask bits.

BUILDING VIRTUAL NETWORKS

In addition to increasing productivity, switches allow you to create virtual networks. One of the methods for creating a virtual network is to create a broadcast domain through a logical connection of ports within the physical infrastructure of a communication device (this can be either a smart hub - configuration switching or a switch - frame switching). For example, the odd ports of an eight-port device are assigned to one virtual network, and the even ports are assigned to another. As a result, a station in one virtual network becomes isolated from stations in another. The disadvantage of this method of organizing a virtual network is that all stations connected to the same port must belong to the same virtual network.

Another method for creating a virtual network is based on the MAC addresses of connected devices. With this method of organizing a virtual network, any employee can connect, for example, his laptop computer to any switch port, and it will automatically determine whether his user belongs to a particular virtual network based on the MAC address. This method also allows users connected to the same switch port to belong to different virtual networks. Read more about virtual networks see the article by A. Avduevsky “Such real virtual networks” in the March issue of LAN for this year.

LEVEL 3 SWITCHING

For all their advantages, switches have one significant drawback: they are unable to protect the network from avalanches of broadcast packets, and this leads to unproductive network load and increased response time. Routers can monitor and filter unnecessary broadcast traffic, but they are orders of magnitude slower. Thus, according to Case Technologies documentation, the typical performance of a router is 10,000 packets per second, and this cannot be compared with the same indicator of a switch - 600,000 packets per second.

As a result, many manufacturers have begun to build routing functionality into switches. To prevent the switch from slowing down significantly, various methods are used: for example, both Layer 2 switching and Layer 3 switching are implemented directly in hardware(V integrated circuits ASIC). Various manufacturers This technology is called differently, but the goal is the same: the routing switch must perform third-level functions at the same speed as second-level functions. An important factor is the price of such a device per port: it should also be low, like that of switches (see article by Nick Lippis in the next issue of LAN magazine).

CONCLUSION

Switches are both structurally and functionally very diverse; It is impossible to cover all their aspects in one short article. In the next tutorial, we'll take a closer look at ATM switches.

Dmitry Ganzha is the executive editor of LAN. He can be contacted at: [email protected].

Switches in the local network