Building a home network. What's smart about smart network switches? Basics of bridges and switches Why do you need a switch in a local network?
Issues of building local networks seem very complex to non-specialist users due to the extensive terminological dictionary. Hubs and switches are imagined as complex equipment reminiscent of telephone exchanges, and the creation of a local home network becomes a reason to turn to specialists. In fact, the switch is not as scary as its name: both devices are elementary network nodes that have minimal functionality, do not require knowledge of installation and operation, and are quite accessible to everyone.
Definition
Hub— a network hub designed to connect computers into a single local network by connecting Ethernet cables.
Switch(switch) is a network switch designed to connect several computers into a local network via an Ethernet interface.
Comparison
As we can see from the definition, the difference between a hub and a switch is related to the type of device: hub and switch. Despite one task - organizing a local network via Ethernet - devices approach its solution in different ways. A hub is a simple splitter that provides a direct connection between network clients. A switch is a more “smart” device that distributes data packets between clients in accordance with the request.
The hub, receiving a signal from one node, transmits it to all connected devices, and reception depends entirely on the recipient: the computer itself must recognize whether the packet is intended for it. Naturally, the answer assumes the same pattern. The signal pokes into all segments of the network until it finds one that will receive it. This circumstance reduces network throughput (and data exchange speed, respectively). The switch, receiving a data packet from the computer, sends it exactly to the address that was specified by the sender, relieving the network of load. A network organized through a switch is considered more secure: traffic exchange occurs directly between two clients, and others cannot process a signal that is not intended for them. Unlike a hub, a switch provides high throughput of the created network.
Logitec LAN-SW/PS Hub
The switch requires correct configuration of the network card of the client computer: the IP address and subnet mask must match each other (the subnet mask indicates part of the IP address as the network address, and the other part as the client address). The hub does not require any settings, because it works at the physical level of the OSI network model, broadcasting a signal. The switch operates at the channel level, exchanging data packets. Another feature of the hub is the equalization of nodes in terms of data transfer speed, focusing on the lowest rates.
Switch COMPEX PS2208B Conclusions website
- Hub is a hub, switch is a switch.
- The hub device is the simplest, the switch is more “intelligent”.
- The hub transmits the signal to all network clients, the switch only to the recipient.
- The performance of a network organized through a switch is higher.
- The switch provides a higher level of data transmission security.
- The hub operates at the physical layer of the OSI network model, the switch at the channel layer.
- The switch requires proper configuration of network cards of network clients.
The switch is one of the most important devices used in building a local network. In this article we will talk about what switches are and focus on the important characteristics that need to be taken into account when choosing a local network switch.
First, let's look at the general block diagram to understand what place the switch occupies in the enterprise local network.
The figure above shows the most common block diagram of a small local network. As a rule, access switches are used in such local networks.
Access switches are directly connected to end users, providing them with access to local network resources.
However, in large local networks, switches perform the following functions:
Network access level. As mentioned above, access switches provide connection points for end-user devices. In large local networks, access switch frames do not communicate with each other, but are transmitted through distribution switches.
Distribution level. Switches at this layer forward traffic between access switches, but do not interact with end users.
System kernel level. Devices of this type combine data transmission channels from distribution level switches in large territorial local networks and provide very high speed switching of data flows.
Switches are:
Unmanaged switches. These are ordinary stand-alone devices on a local network that manage data transfer independently and do not have the possibility of additional configuration. Due to ease of installation and low price, they are widely used for installation at home and in small businesses.
Managed Switches. More advanced and expensive devices. They allow the network administrator to independently configure them for specified tasks.
Managed switches can be configured in one of the following ways:
Via console port Via WEB interface
Through Telnet Via SNMP protocol
Via SSH
Switch levels
All switches can be divided into model levels OSI . The higher this level, the greater the capabilities the switch has, however, its cost will be significantly higher.
Layer 1 switches. This level includes hubs, repeaters and other devices operating at the physical level. These devices were present at the dawn of the development of the Internet and are currently not used on the local network. Having received a signal, a device of this type simply transmits it further to all ports except the sender port
Layer 2 switches2) . This level includes unmanaged and some managed switches ( switch ) working at the link level of the model OSI . Second-level switches work with frames - frames: a stream of data divided into portions. Having received the frame, the layer 2 switch reads the sender's address from the frame and enters it into its table MAC addresses, matching this address to the port on which it received this frame. Thanks to this approach, Layer 2 switches forward data only to the destination port, without creating excess traffic on other ports. Layer 2 switches don't understand IP addresses located at the third network level of the model OSI and work only at the link level.
Layer 2 switches support the most common protocols such as:
IEEE 802.1 q or VLAN virtual local networks. This protocol allows you to create separate logical networks within the same physical network.
For example, devices connected to the same switch, but located in different VLAN will not see each other and will be able to transmit data only in their own broadcast domain (devices from the same VLAN). Between themselves, the computers in the figure above will be able to transmit data using a device operating at the third level with IP addresses: router.
IEEE 802.1p (Priority tags ). This protocol is natively present in the protocol IEEE 802.1q and is a 3-bit field from 0 to 7. This protocol allows you to mark and sort all traffic by importance by setting priorities (maximum priority 7). Frames with higher priority will be forwarded first.
IEEE 802.1d Spanning tree protocol (STP).This protocol builds a local network in the form of a tree structure to avoid network loops and prevent the formation of a network storm.
Let's say the local network is installed in the form of a ring to increase the fault tolerance of the system. The switch with the highest priority in the network is selected as the root switch.In the example above, SW3 is the root. Without delving into protocol execution algorithms, switches calculate the path with the maximum cost and block it. For example, in our case, the shortest path from SW3 to SW1 and SW2 will be through its own dedicated interfaces (DP) Fa 0/1 and Fa 0/2. In this case, the default path price for the 100 Mbit/s interface will be 19. Interface Fa 0/1 of the local network switch SW1 is blocked because the total path price will be the sum of two transitions between 100 Mbit/s interfaces 19+19=38.
If the working route is damaged, the switches will recalculate the path and unblock this port
IEEE 802.1w Rapid spanning tree protocol (RSTP).Enhanced 802.1 standard d , which has higher stability and shorter recovery time of the communication line.
IEEE 802.1s Multiple spanning tree protocol.The latest version, taking into account all the shortcomings of the protocols STP and RSTP.
IEEE 802.3ad Link aggregation for parallel link.This protocol allows you to combine ports into groups. The total speed of a given aggregation port will be the sum of the speeds of each port in it.The maximum speed is determined by the IEEE 802.3ad standard and is 8 Gbit/s.
Layer 3 switches3) . These devices are also called multiswitches since they combine the capabilities of switches operating at the second level and routers operating with IP packages at the third level.Layer 3 switches fully support all the features and standards of Layer 2 switches. Network devices can be accessed using IP addresses. A layer 3 switch supports the establishment of various connections: l 2 tp, pptp, pppoe, vpn, etc.
Layer 4 switches 4) . L4 level devices operating at the transport layer model OSI . Responsible for ensuring the reliability of data transmission. These switches can, based on information from packet headers, understand whether traffic belongs to different applications and make decisions about redirecting such traffic based on this information. The name of such devices is not settled; sometimes they are called smart switches, or L4 switches.
Main characteristics of switches
Number of ports. Currently, there are switches with the number of ports from 5 to 48. The number of network devices that can be connected to a given switch depends on this parameter.
For example, when building a small local network of 15 computers, we will need a switch with 16 ports: 15 for connecting end devices and one for installing and connecting a router to access the Internet.
Data transfer rate. This is the speed at which each switch port operates. Typically speeds are specified as follows: 10/100/1000 Mbit/s. The speed of the port is determined during auto negotiation with the end device. On managed switches, this parameter can be configured manually.
For example : A PC client device with a 1 Gbps network card is connected to a switch port with an operating speed of 10/100 Mbps c . As a result of auto-negotiation, devices agree to use the maximum possible speed of 100 Mbps.
Auto port negotiation between Full – duplex and half – duplex. Full – duplex: Data transfer is carried out simultaneously in two directions. Half-duplex Data transmission is carried out first in one direction, then in the other direction sequentially.
Internal fabric bandwidth. This parameter shows the overall speed at which the switch can process data from all ports.
For example: on a local network there is a switch with 5 ports operating at a speed of 10/100 Mbit/s. In the technical specifications, the switching matrix parameter is 1 Gbit/ c . This means that each port is in Full-duplex can operate at a speed of 200 Mbit/ c (100 Mbit/s reception and 100 Mbit/s transmission). Let's assume that the parameter of this switching matrix is less than the specified one. This means that during peak loads, the ports will not be able to operate at the declared speed of 100 Mbit/s.
Auto MDI/MDI-X cable type negotiation. This function allows you to determine which of the two methods the EIA/TIA-568A or EIA/TIA-568B twisted pair was crimped. When installing local networks, the EIA/TIA-568B scheme is most widely used.
Stacking is the combination of several switches into one single logical device. Different switch manufacturers use their own stacking technologies, e.g. c isco uses Stack Wise stacking technology with a 32 Gbps bus between switches and Stack Wise Plus with a 64 Gbps bus between switches.
For example, this technology is relevant in large local networks, where it is necessary to connect more than 48 ports on the basis of one device.
Mounting for 19” rack. In home environments and small local networks, switches are often installed on flat surfaces or mounted on the wall, but the presence of so-called “ears” is necessary in larger local networks where active equipment is located in server cabinets.
MAC table sizeaddresses A switch is a device operating at level 2 of the model OSI . Unlike a hub, which simply redirects the received frame to all ports except the sender port, the switch learns: remembers MAC address of the sender's device, entering it, port number and lifetime of the entry into the table. Using this table, the switch does not forward the frame to all ports, but only to the recipient port. If the number of network devices in the local network is significant and the table size is full, the switch begins to overwrite older entries in the table and writes new ones, which significantly reduces the speed of the switch.
Jumboframe . This feature allows the switch to handle larger packet sizes than those defined by the Ethernet standard. After each packet is received, some time is spent processing it. When using an increased packet size using Jumbo Frame technology, you can save on packet processing time in networks that use data transfer rates of 1 Gb/sec and higher. At a lower speed there is no big gain
Switching modes.In order to understand the principle of operation of switching modes, first consider the structure of the frame transmitted at the data link level between the network device and the switch on the local network:
As can be seen from the picture:
- First comes the preamble signaling the start of frame transmission,
- Then MAC destination address ( DA) and MAC sender's address ( S.A.)
- Third level ID: IPv 4 or IPv 6 is used payload)
- And at the end the checksum FCS: A 4 byte CRC value used to detect transmission errors. Calculated by the sending party, and placed in the FCS field. The receiving party calculates this value independently and compares it with the received value.
Now let's look at the switching modes:
Store - and - forward. This switching mode saves the entire frame to a buffer and checks the field FCS , which is at the very end of the frame and if the checksum of this field does not match, discards the entire frame. As a result, the likelihood of network congestion is reduced, since it is possible to discard frames with errors and delay the transmission time of the packet. This technology is present in more expensive switches.
Cut-through. Simpler technology. In this case, frames can be processed faster, since they are not completely saved to the buffer. For analysis, data from the beginning of the frame to the destination MAC address (DA), inclusive, is stored in a buffer. The switch reads this MAC address and forwards it to the destination. The disadvantage of this technology is that the switch in this case forwards both dwarf packets with a length of less than 512 bit intervals and damaged packets, increasing the load on the local network.
PoE technology support
Pover over ethernet technology allows you to power a network device over the same cable. This solution allows you to reduce the cost of additional installation of supply lines.
The following PoE standards exist:
PoE 802.3af supports equipment up to 15.4 W
PoE 802.3at supports equipment up to 30W
Passive PoE
PoE 802.3 af/at have intelligent control circuits for supplying voltage to the device: before supplying power to the PoE device, the af/at standard source negotiates with it to avoid damage to the device. Passiv PoE is much cheaper than the first two standards; power is directly supplied to the device via free pairs of the network cable without any coordination.
Characteristics of standards
The PoE 802.3af standard is supported by most low-cost IP cameras, IP phones and access points.
The PoE 802.3at standard is present in more expensive models of IP video surveillance cameras, where it is not possible to meet 15.4 W. In this case, both the IP video camera and the PoE source (switch) must support this standard.
Expansion slots. Switches may have additional expansion slots. The most common are SFP modules (Small Form-factor Pluggable). Modular, compact transceivers used for data transmission in a telecommunications environment.
SFP modules are inserted into a free SFP port of a router, switch, multiplexer or media converter. Although SFP Ethernet modules exist, the most commonFiber optic modules are used to connect the main channel when transmitting data over long distances beyond the reach of the Ethernet standard. SFP modules are selected depending on distance and data transfer speed. The most common are dual-fiber SFP modules, which use one fiber for receiving and the other for transmitting data. However, WDM technology allows data transmission at different wavelengths over a single optical cable.
SFP modules are:
- SX - 850 nm used with multimode optical cable over distances up to 550m
- LX - 1310 nm is used with both types of optical cable (SM and MM) at a distance of up to 10 km
- BX - 1310/1550 nm is used with both types of optical cable (SM and MM) at a distance of up to 10 km
- XD - 1550 nm is used with single mode cable up to 40 km, ZX up to 80 km, EZ or EZX up to 120 km and DWDM
The SFP standard itself provides for data transmission at a speed of 1 Gbit/s, or at a speed of 100 Mbit/s. For faster data transfer, SFP+ modules were developed:
- SFP+ data transfer at 10 Gbps
- XFP data transfer at 10 Gbps
- QSFP+ data transfer at 40 Gbps
- CFP data transfer at 100 Gbps
However, at higher speeds, signals are processed at high frequencies. This requires greater heat dissipation and, accordingly, larger dimensions. Therefore, in fact, the SFP form factor is still preserved only in SFP+ modules.
Conclusion
Many readers have probably come across unmanaged switches and low-cost managed layer 2 switches in small local networks. However, the choice of switches for building larger and more technically complex local networks is best left to professionals.
Safe Kuban uses switches of the following brands when installing local networks:
Professional Solution:
Cisco
Qtech
Budget solution
D-Link
Tp-Link
Tenda
Safe Kuban carries out installation, commissioning and maintenance of local networks in Krasnodar and the South of Russia.
To create a local or home network, you need special devices. From this article you will learn a little about them. I will try to explain as simply as possible so that everyone can understand.
Purpose .
Hub, switch and router are designed to create a network between computers. Of course, after creation, this network will also function.
Difference .
What is a hub
A hub is a repeater. Everything that is connected to it will be repeated. One is given to the hub and therefore everything is connected.
For example, you connected 5 computers through the Hub. To transfer data from the fifth computer to the first, the data will pass through all the computers on the network. It's like a parallel phone - any computer can access your data, and so can you. Due to this, the load and distribution also increases. Accordingly, the more computers are connected, the slower the connection will be and the greater the load on the network. This is why nowadays fewer and fewer hubs are being produced and less and less are being used. Soon they will completely disappear.
What is a switch?
The switch replaces the hub and corrects the shortcomings of its predecessor. Each connected to the switch has its own separate IP address. This reduces the load on the network and each computer will receive only what it needs and others will not know about it. But the switch has a disadvantage associated with dignity. The fact is that if you want to divide the network into more than 2 computers, then you will need more IP addresses. This usually depends on the provider, and they usually only provide one IP address.
What is a router?
Router - it is often also called a router. Why? Yes, because it is a link between two different networks and transmits data based on a specific route specified in its routing table. To put it very simply, the router is an intermediary between your network and Internet access. The router corrects all the mistakes of its predecessors and that is why it is the most popular nowadays. Especially considering the fact that routers are often equipped with Wi-Fi antennas for transmitting the Internet to wireless devices, and also have the ability to connect USB modems.
The router can be used either separately: PC -> router -> Internet, or together with other devices: PC -> switch/hub -> router -> Internet.
Another advantage of the router is its easy installation. Often, only minimal knowledge is required from you to connect, configure a network and access the Internet.
So. Let me summarize briefly.
All these devices are needed to create a network. Hub and switch are not very different from each other. A router is the most necessary and convenient solution for creating a network.
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. The ports use a bandwidth sharing approach, which often results in reduced performance on the LAN 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.
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 communications through the 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). 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 LAN switching, uses standard Ethernet (or Token Ring) frame formats. 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 be simultaneously guaranteed 10 Mbps throughput. 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 (except for 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.
Picture 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 provide end-to-end switching, but 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, so 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. The modules of such a switch perform switching between networks of 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.
Cell switching is increasingly being used in high-end switches 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. For more information 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 capabilities into switches. To prevent the switch from being significantly slowed down, various techniques are used: for example, both Layer 2 switching and Layer 3 switching are implemented directly in hardware (ASICs). Different manufacturers call this technology differently, but the goal is the same: the routing switch must perform Layer 3 functions at the same speed as Layer 2 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