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 dwell on the important characteristics that you need to consider when choosing a LAN switch.
First, let's look at a general block diagram in order to understand what place the switch occupies in the local network of an enterprise.
The figure above shows the most common block diagram of a small local area network. As a rule, access switches are used in such local networks.
Access switches are directly connected to end users, giving them access to local network resources.
However, in large local area networks, switches perform the following functions:
Network access level... As mentioned above, access switches provide connection points for end-user devices. In large local area networks, the frames of the access switches do not interact with each other, but are transmitted through the distribution switches.
Distribution level... Switches of this layer forward traffic between access switches, but they do not interact with end users.
System kernel level... Devices of this type combine data transmission channels from switches of the distribution level in large local area networks and provide a very high speed of switching data streams.
Switches are:
Unmanaged switches. These are ordinary stand-alone devices in the local network that manage the data transfer on their own and do not have the possibility of additional configuration. Due to the ease of installation and low price, they are widely used for installation at home and small businesses.
Managed switches... More advanced and expensive devices. Allows the network administrator to independently configure them for specified tasks.
Managed switches can be configured in one of the following ways:
Through the console port Via WEB interface
Across Telnet Via SNMP
Through SSH
Switch levels
All switches can be categorized into model levels OSI ... The higher this level is, the more capabilities the switch has, however, its cost will be much higher.
Layer 1 switches... This level includes hubs, repeaters and other devices operating at the physical level. These devices were at the dawn of the development of the Internet and are currently not used in the local network. Having received a signal, a device of this type simply transmits it further, to all ports, except for the sender's port.
Layer 2 switches (layaer2). This level includes unmanaged and some managed switches ( switch ) working at the link level of the model OSI ... Layer 2 switches work with frames - frames: a stream of data divided into chunks. Having received the frame, the Layer 2 switch subtracts the sender's address from the frame and enters it into its table MAC addresses, matching this address to the port on which he received this frame. Thanks to this approach, Layer 2 switches forward data only to the destination port, without creating excessive traffic on other ports. Layer 2 switches don't understand IP addresses located on the third network level of the model OSI and work only at the data link layer.
Layer 2 switches support the most common protocols such as:
IEEE 802.1 q or VLAN virtual local area networks. This protocol allows creating separate logical networks within one 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 broadcast domain (to devices from the same VLAN). Computers in the figure above will be able to transfer data between themselves using a device operating at the third level with IP addresses: router.
IEEE 802.1p (Priority tags ). This protocol is initially 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 in order of 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 a tree structure to avoid network loops and prevent network storms from forming.
Let's say the installation of a local network is made in the form of a ring to increase the fault tolerance of the system. The switch with the highest priority on the network is selected as the Root.In the example above, SW3 is the root. Without going deep into the algorithms for executing the protocol, the 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 cost for the 100 Mbps interface will be 19. The Fa 0/1 interface of the LAN switch SW1 is blocked because the total path cost will be the sum of two hops between 100 Mbps 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 link recovery time.
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 this 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 Gbps.
Layer 3 switches (layer3). These devices are also called multiswitches because 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 functions and standards of Layer 2 switches. Network devices can be operated by IP addresses. The Layer 3 switch supports the establishment of various connections: l 2 tp, pptp, pppoe, vpn, etc.
Layer 4 switches 4) . L4 devices operating at the transport level of the model OSI ... Responsible for ensuring the reliability of data transmission. These switches can, based on information from the packet headers, understand the traffic belonging to different applications and make decisions about redirecting such traffic based on this information. The name of such devices has not settled down, sometimes they are called smart switches, or L4 switches.
Key features 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 this switch depends on this parameter.
For example, when building a small local network of 15 computers, we need a switch with 16 ports: 15 for connecting end devices and one for installing and connecting a router to access the Internet.
Baud rate. This is the speed at which each port on the switch operates. Typically, speeds are indicated as follows: 10/100/1000 Mbps. The port speed is determined during auto-negotiation with the end device. In managed switches, this parameter can be manually configured.
For example : Client device PC with 1 Gbps NIC is connected to the switch port at 10/100 Mbps c ... As a result of auto-negotiation, the devices agree to use the maximum possible speed of 100 Mbps.
Auto port negotiation between Full - duplex and half - duplex. Full - duplex: data transmission is carried out simultaneously in two directions. Half - duplex data transmission is carried out first in one, then in the other direction sequentially.
Internal bandwidth of the switch fabric... This parameter shows at what general speed the switch can process data from all ports.
For example: in a local network there is a switch with 5 ports operating at a speed of 10/100 Mbps. In the technical specifications, the parameter switching matrix is 1 Gbit / c ... This means that each port is in Full - duplex can work at a speed of 200 Mbps c (100 Mbps receive and 100 Mbps transmit). Let the parameter of the given switching matrix be less than the specified one. This means that at the time of peak loads, the ports will not be able to operate at the declared speed of 100 Mbps.
Auto negotiation of MDI / MDI-X cable type... This function allows you to determine which of the two methods was used to crimp an EIA / TIA-568A or EIA / TIA-568B twisted pair. When installing local networks, the EIA / TIA-568B scheme was most widespread.
Stacking Is the combination of several switches into one single logical device. Different switch manufacturers use their own stacking technologies, for example c isco uses Stack Wise stacking technology with a 32 Gbps bus and Stack Wise Plus with a 64 Gbps bus between switches.
For example, this technology is relevant in large local networks, where it is required to connect more than 48 ports on the basis of one device.
19 ”rack mount... At home and small local area networks, switches are often installed on flat surfaces or mounted on a wall, but the presence of so-called "ears" is necessary in larger local area networks where active equipment is located in server cabinets.
MAC table sizeaddresses. Switch (switch) is a device operating at the 2nd level of the model OSI ... Unlike the hub, which simply redirects the received frame to all ports except the sender's port, the switch learns: remembers MAC the address of the sender device, entering it, the port number and the lifetime of the entry in the table. Using this table, the switch does not redirect the frame to all ports, but only to the destination port. If the number of network devices in the local network is significant and the size of the table is full, the switch starts overwriting the older entries in the table and writes new ones, which significantly reduces the speed of the switch.
Jumboframe ... This feature allows the switch to operate with a larger packet size than specified by the Ethernet standard. After receiving each packet, it takes some time to process it. When using the increased packet size using the Jumbo Frame technology, you can save on packet processing time in networks where data transfer rates from 1 Gb / s and higher are used. At a lower speed, there is no big win
Switching modes.In order to understand the principle of operation of switching modes, first consider the structure of the frame transmitted at the link layers between the network device and the switch in the local network:
As you can see from the picture:
- First comes the preamble signaling the beginning of the frame transmission,
- Then MAC destination address ( DA) and MAC sender address ( SA)
- Third level identifier: IPv 4 or IPv 6 is in use payload)
- And at the end the checksum FCS: A 4 byte CRC value used to detect transmission errors. Calculated by the sender and placed in the FCS field. The receiving side 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 the 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 congestion in the network is reduced, since it is possible to drop frames with an error and postpone the transmission time of the packet. This technology is found 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 saved to the buffer. The switch reads this MAC address and forwards it to the destination. The disadvantage of this technology is that the switch is sending in this case both dwarf packets with a length of less than 512 bit intervals and damaged packets, increasing the load on the local network.
PoE 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.
PoE standards are as follows:
PoE 802.3af supports equipment up to 15.4W
PoE 802.3at supports equipment up to 30W
Passiv PoE
PoE 802.3 af / at has intelligent control circuits for supplying voltage to the device: before supplying power to the PoE device, the af / at 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 through free pairs of network cable without any coordination.
Characteristics of standards
PoE 802.3af 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 CCTV cameras, where it is not possible to keep within 15.4 watts. In this case, both the IP video camera and the PoE source (switch) must support this standard.
Expansion slots... Switches can have additional expansion slots. The most common are SFP modules (Small Form-factor Pluggable). Modular, compact transceivers used for data transmission in telecommunication environments.
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, unattainable for the Ethernet standard. SFP modules are selected depending on the distance, data transfer rate. 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 - 850nm used with multimode optical cable 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 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 transfer at a speed of 1 Gbps, or at a speed of 100 Mbps. For faster data transfer, SFP + modules have been 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 higher frequencies. This requires more heat dissipation and, accordingly, larger dimensions. Therefore, in fact, the SFP form factor has survived only in SFP + modules.
Conclusion
Many readers have probably come across unmanaged switches and budget managed L2 switches in small local area networks. However, the choice of switches for building larger and more technically complex local networks is better 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.
Connecting the Internet to an apartment or a private house always raises many questions. To begin with, we choose an Internet provider if there is a lot to choose from. After that we look closely at the tariffs, and only then we try to find out how the switch differs from the router.
Equipment
Both devices belong to They are designed for the functioning of computer networks. These include not only a switch and a router, but also a hub, patch panel, etc. Anyone can be assigned to one of the groups: active or passive. You need to understand what is the difference between them.
Active
These devices are built on electronic circuits that receive electrical power. Such equipment is designed to amplify and convert the signal. The main characteristic is the use of special algorithms for processing. What does it mean?
The Internet network works with batch sending of files. Each such set has its own technical parameters: this includes materials about its sources, purposes, data integrity, etc. These indicators make it possible to transfer packets to the desired address.
An active device not only finds a signal, but also processes these technical parameters. It directs them downstream according to built-in algorithms. This skill enables the apparatus to be called such.
Passive
This group is not receiving the required power from the mains. Works with distribution and reduction of signal levels. These devices can safely include cables, plug and socket, balun, patch panel. Some attribute it to telecommunication cabinets, cable trays, etc.
Variety
Since the network is active mainly thanks to the first group of devices, we will talk about it. This includes ten different types of devices. For example, a network adapter that is located in the computer itself. Network equipment of this type is now found in all PCs and helps to connect to the LAN.
This also includes a repeater. The device has two ports and works with signal duplication. In this way, it helps to increase the size of the network segment. A hub is also an active piece of equipment, sometimes referred to as a hub. It operates with 4-32 channels and serves for the interaction of all participants in the network.
And finally, we got to the question of how a switch differs from a router. Although besides them, there is also a repeater, a media converter, a bridge and a network transceiver.
Router
So let's start with this device. People simply call it a router. It serves to forward packets between different network segments. In this case, it is guided by the rules and routing tables. The device connects networks with different architectures. In order to correctly complete the process, it studies the typology, determines the rules set by the administrator.
To understand the question of how a switch differs from a router, it is important to understand the principles of operation of one and the second device. So, the router first examines the information about the recipient: it looks at his address and the name of the set. Then it goes to and identifies the path for transferring files. If the tables do not contain the required information, the data packets are discarded.
Sometimes other methods can be used to select the desired path. For example, the sender's address, the upper-layer protocols and all the data that is hidden behind the name of the set are examined.
Routers interact with address translation, filter transit streams according to prescribed rules, encrypt or decrypt transmitted files.
Switch
A network switch or switch is a device that interacts with the connection of several PC network nodes. The whole process does not go beyond several or one part of the network.
This equipment also belongs to the active group. It operates at the OSI data link layer. Since the switch was originally configured to work with bridging parameters, it can be considered as a multiport bridge. To combine several lines at the network level, just a router is used.
The switch has no control over the distribution of traffic from one gadget to the rest. It only conveys information to the right person. The process has good performance and keeps the internet safe.
The switch's job is to store the switching table and, using it, determine the correspondence between MAC addresses. When the equipment is connected, the table is empty and is filled in as the device learns itself.
Files that go to one of the ports are immediately sent through other channels. The device begins to examine the frames and, after determining the sender's addresses, temporarily enters the information into the archive. When a port receives a frame, the address of which has already been recorded, it will be transmitted along the path specified in the configuration.
Difference
How is a switch different from a router? At first glance, it is definitely worth saying that the main differences of these devices lie in the principles of operation. There is a rather interesting analogy that easily explains the difference.
Let's say we have a corporate mail server. The employee sent the file, which must reach the recipient through an internal or local delivery system. In this case, the switch is the mail server, and the router is local.
What we have? The switch does not analyze mail content and type. It keeps a list of all employees of the company, the addresses of their offices. Therefore, its main task is to send mail to a specific addressee.
In this whole story, the router works as a postman to deliver information to people who work outside the company. He checks the content and can independently change the delivery rules if any additional information is found in the letter.
The disadvantage of a router compared to a switch lies in the complex and costly administration. Specialists who work with this equipment must own a huge number of parameters. In this case, the configuration must always be consistent with another configuration in the network.
conclusions
Most companies are trying to modernize their network, so they are replacing outdated equipment with a switch between routers and networks. New devices help improve productivity, and their legacy counterparts continue to work on security.
Configuring a router and switch is not easy. It is generally better for an ordinary user not to go here. When setting up a home network, specialists come to install this equipment and configure it in parallel. This process is not easy. It is individual for each provider and specific network.
If there are any failures, then you need to contact your Internet provider, because if there are problems with the configuration, then you cannot cope without it.
03/18/1997 Dmitry Ganzha
Switches are central to today's LANs. TYPES OF SWITCHING SWITCHING HUBS METHODS OF PROCESSING RISC AND ASIC PACKAGES ARCHITECTURE OF HIGH CLASS SWITCHES CONSTRUCTION OF VIRTUAL NETWORKS LEVEL THIRD SWITCHING CONCLUSION is one of the most popular technologies.
Switches are central to today's LANs.
Switching is one of the most popular modern technologies. Switches are replacing bridges and routers at the edge of local networks, leaving behind them the role of organizing communication over the global network. Such popularity of switches is primarily due to the fact that they allow, due to micro-segmentation, to increase network performance compared to shared networks with the same nominal bandwidth. In addition to dividing the network into small segments, switches provide the ability to organize connected devices into logical networks and easily rearrange them when necessary; in other words, they allow the creation of virtual networks.
What is a switch? According to IDC's definition, "a switch is a device designed as a hub and acting as a high-speed multiport bridge; the built-in switching mechanism allows segmenting the local network and allocating 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 refers primarily to frame switches.
TYPES OF SWITCHING
Switching generally refers to four different technologies — configuration switching, frame switching, cell switching, and frame-to-cell conversion.
Configuration switching is also known as port switching, whereby a specific port on the Smart Hub module is assigned to one of the internal Ethernet (or Token Ring) segments. This assignment is done remotely through programmatic network management when users and resources on the network connect or move. 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 along the network directly to the recipient. As a result, the network turns, as it were, into a set of parallel operating high-speed direct channels. We will consider how frame switching within a switch is carried out 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 cell switches can support multiple independent workgroups regardless of their physical connectivity (see the Building Virtual Networks section).
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 personnel switching.
SWITCHING CONCENTRATORS
The first switching hub, EtherSwictch, was introduced by Kalpana. This hub reduced network contention by reducing the number of nodes in a logical segment using micro-segmentation 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 across the bridge, but without the delay inherent in the bridge.
In a switched Ethernet network, each member of a group of several users can be guaranteed a bandwidth of 10 Mbps at the same time. Understanding how such a hub works is best helped by analogy with an ordinary old telephone switch, in which a coaxial cable connects the conversation participants. When a subscriber called on "perpetual" 07 and asked to connect him to such and such a number, the operator first of all checked whether the line was available; if so, he connected the participants directly with a piece of cable. No one else (with the exception of the special services, of course) could hear their conversation. After finishing the call, the operator disconnected the cable from both ports and waited for the next call.
Switching hubs work in a similar way (see Figure 1): they forward packets from the ingress port to the egress port through the switch fabric. When a packet hits an ingress port, the switch reads its MAC address (that is, a Layer 2 address) and it is immediately forwarded to the port associated with that address. If the port is busy, the packet is queued. Essentially, a queue is a buffer on an input port where packets wait for the correct port to be released. However, the buffering methods are slightly different.
Picture 1.
Switching hubs function similarly to legacy telephone switches: they connect the upstream port directly to the downstream port through the switch fabric.
PACKAGE PROCESSING METHODS
In end-to-end switching (also called on-the-fly switching and bufferless switching), the switch only reads 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 the processing time of the packet, since only the first few bytes are read. Therefore, it is up to the receiving side to identify defective packets and request their retransmission. However, modern cabling systems are reliable enough that the need for retransmission on many networks is minimal. However, no one is immune from errors in the event of cable damage, network board malfunction, or interference from an external electromagnetic source.
In buffer switching, the switch, receiving a packet, does not forward it until it reads it in full, or at least reads all the information it needs. It not only determines the recipient's address, but also checks the checksum, that is, it can cut off defective packets. This allows you to isolate the segment that is causing the error. Thus, float switching places an emphasis on reliability over speed.
In addition to the above two, some switches use a hybrid method. Under normal circumstances, they carry out end-to-end switching, but at the same time monitor the number of errors by checking checksums. If the number of errors reaches a predetermined threshold value, they go into buffered switching mode. When the number of errors decreases to an acceptable level, they return to the end-to-end switching mode. This type of switching is called threshold or adaptive switching.
RISC AND ASIC
Buffer switches are often implemented using standard RISC processors. One of the advantages of this approach is that they are relatively cheap compared to switches with ASICs, 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. The disadvantage is that they are slower than ASIC-based switches.
Switches with integrated circuits ASICs are designed to perform specialized tasks: all their functionality is "wired" into the hardware. There is also a drawback to this approach: when an upgrade is needed, the manufacturer is forced to rework the circuit. ASICs are usually end-to-end switching. The ASIC fabric creates dedicated physical paths between the input and output ports, as shown in.
ARCHITECTURE OF HIGH CLASS SWITCHES
High-end switches are generally modular and can handle both packet switching and cell switching. The modules of such a switch carry out switching between networks of different types, including Ethernet, Fast Ethernet, Token Ring, FDDI and ATM. At the same time, the main switching mechanism in such devices is the ATM switching structure. We will look at the architecture of such devices using the example of the Centillion 100 from Bay Networks.
Switching is done using the following three hardware components (see Figure 2):
(1x1)
Figure 2.
High-end switches are increasingly using cell switching due to their 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 for frame switching between local ports and a packet collector / decompressor for converting frames and cells to each other. All modules can independently switch between their ports so that only traffic destined for other modules is passed through the backplane.
Each module maintains its own address table, and the main control processor brings them together 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 to whom the packet is addressed. If the address is in the local address table, then the RISC processor switches the packet between local ports. If the target is on another module, then the collector / parser converts the packet to cells. The CellManager specifies a destination mask to identify the module (s) and port (s) to which the cell payload is destined. Any module whose board mask bit is specified in the destination mask copies the cell to local memory and transmits data to the corresponding output port in accordance with the specified port mask bits.
BUILDING VIRTUAL NETWORKS
In addition to improving performance, 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 an intelligent hub - configuration switching, or a switch - frame switching). For example, the odd-numbered ports on an eight-port device are assigned to one virtual network, and the even-numbered ports are assigned to another. As a result, a station in one virtual network is 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 of creating a virtual network is based on the MAC addresses of the connected devices. With this method of organizing a virtual network, any employee can connect, for example, his laptop to any port of the switch, and he will automatically determine the belonging of his user 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 details on virtual networks, see A. Avduevsky's article "Such real virtual networks" in the March issue of LAN for this year.
THIRD LEVEL SWITCHING
For all their advantages, switches have one significant drawback: they cannot protect the network from avalanches of broadcast packets, and this leads to unproductive network load and an increase in response time. Routers can monitor and filter unnecessary broadcast traffic, but they are orders of magnitude slower. For example, according to Case Technologies documentation, the typical router performance is 10,000 packets per second, which is no match for a switch's 600,000 packets per second.
As a result, many vendors have started to build routing functionality into switches. To ensure that the operation of the switch does not slow down significantly, various methods are used: for example, both the second layer switching and the third layer switching are implemented directly in the hardware (in ASICs). Different manufacturers call this technology differently, but the goal is the same: the routing switch must perform the functions of the third layer at the same speed as the functions of the second layer. An important factor is the price of such a device per port: it should also be low, like that of switches (see Nick Lippis's article 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 lesson, we will take a closer look at ATM switches.
Dmitry Ganzha is the executive editor of LAN. You can contact him at: [email protected].
LAN switches
The issues of building local networks seem to be very difficult to non-specialist users due to the extensive terminological vocabulary. Hubs and switches are drawn in the imagination with complex equipment, reminiscent of telephone exchanges, and the creation of a local home network becomes a reason for contacting specialists. In fact, the switch is not as terrible as its name: both devices are elementary network nodes with minimal functionality, do not require knowledge of installation and operation, and are quite accessible to everyone.
Definition
Hub- a network hub designed to unite computers into a single local network by connecting Ethernet cables.
Switch(switch - switch) - a network switch designed to combine several computers into a local network via an Ethernet interface.
Comparison
As you can see from the definition, the difference between a hub and a switch is related to the type of device: a hub and a switch. Despite one problem - the organization of a local network via Ethernet - the devices approach it in different ways. A hub is a simple splitter that provides a direct connection between network clients. A switch is a smarter device that distributes data packets between clients in accordance with the request.
A hub, receiving a signal from one node, transmits it to all connected devices, and the reception depends entirely on the addressee: the computer must itself recognize whether the packet is intended for it. Naturally, the answer assumes the same pattern. The signal pokes into all network segments until it finds one that will receive it. This circumstance reduces the network bandwidth (and the data exchange rate, respectively). The switch, receiving a data packet from the computer, directs it to the exact address that was specified by the sender, relieving the network from the load. A network organized through a switch is considered more secure: traffic is exchanged directly between two clients, and others cannot process a signal that is not intended for them. Unlike a hub, a switch provides a high throughput of the created network.
Logitec LAN-SW / PS Hub
The switch requires correct configuration of the client computer's network card: the IP address and subnet mask must match (the subnet mask specifies part of the IP address as a network address, and the other part as client addresses). The hub does not require settings, because it works at the physical layer of the OSI network model, broadcasting a signal. The switch works at the channel level, exchanging data packets. Another feature of the hub is the equalization of nodes in relation to the data transfer rate, focusing on the lowest rates.
Switch COMPEX PS2208B Conclusions site
- Hub - hub, switch - 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 addressee.
- The performance of a network organized through a switch is higher.
- The switch provides a higher level of data transmission security.
- The hub works at the physical layer of the OSI network model, the switch works at the channel one.
- The switch requires the correct configuration of the network cards of the network clients.
How to choose a switch given the existing variety? The functionality of modern models is very different. You can purchase both a simple unmanaged switch and a multifunctional managed switch, which is not much different from a full-fledged router. An example of the latter is the Mikrotik CRS125-24G-1S-2HND-IN from the new Cloud Router Switch line. Accordingly, the price of such models will be much higher.
Therefore, when choosing a switch, first of all, you need to decide which of the functions and parameters of modern switches you need, and for which you should not overpay. But first, a little theory.
Types of switches
However, if earlier managed switches differed from unmanaged switches, including a wider set of functions, now the difference can only be in the possibility or impossibility of remote control of the device. Otherwise, manufacturers add additional functionality even to the simplest models, often increasing their cost.
Therefore, at the moment, the classification of switches by levels is more informative.
Switch levels
In order to choose the switch that best suits our needs, you need to know its level. This parameter is determined based on which OSI (data transfer) network model the device is using.
- Devices first level using physical data transmission have practically disappeared from the market. If someone else remembers hubs, then this is just an example of the physical layer, when information is transmitted in a continuous stream.
- Level 2... This includes almost all unmanaged switches. The so-called channel network model. Devices divide the incoming information into separate packets (frames, frames), check them and send them to a specific recipient device. The basis for distributing information in Layer 2 switches is MAC addresses. Of these, the switch makes the addressing table, remembering which port corresponds to which MAC address. They don't understand IP addresses.
- Level 3... By choosing such a switch, you get a device that already works with IP addresses. It also supports many other possibilities for working with data: converting logical addresses to physical addresses, network protocols IPv4, IPv6, IPX, etc., pptp, pppoe, vpn connections and others. On the third, network data transmission level, almost all routers and the most "advanced" part of switches work.
- Level 4... The OSI networking model used here is called transport... Even not all routers come with support for this model. Traffic is distributed at an intelligent level - the device can work with applications and, based on the headers of data packets, send them to the desired address. In addition, transport layer protocols, such as TCP, guarantee reliable delivery of packets, preserve a certain sequence of their transmission, and are able to optimize traffic.
Choosing a switch - reading the characteristics
How to choose a switch by parameters and functions? Let's consider what is meant by some of the commonly used designations in the characteristics. The basic parameters include:
Number of ports... Their number varies from 5 to 48. When choosing a switch, it is better to provide a margin for further network expansion.
Base baud rate... Most often we see the designation 10/100/1000 Mbps - the speeds that each port of the device supports. That is, the selected switch can operate at 10 Mbps, 100 Mbps, or 1000 Mbps. There are quite a few models that are equipped with both gigabit and 10/100 Mb / s ports. Most modern switches work according to the IEEE 802.3 Nway standard, automatically detecting the port speed.
Bandwidth and internal bandwidth. The first quantity, also called a switching matrix, is the maximum amount of traffic that can be passed through the switch per unit of time. It is calculated very simply: number of ports x port speed x 2 (duplex). For example, an 8-port Gigabit switch has a bandwidth of 16 Gbps.
Internal throughput is usually indicated by the manufacturer and is only needed for comparison with the previous value. If the declared internal bandwidth is less than the maximum, the device will not cope well with heavy loads, slow down and freeze.
Auto MDI / MDI-X detection... This is auto-sensing and support for both standards that twisted pair has been crimped against, without the need for manual control of the connections.
Expansion slots... Possibility of connecting additional interfaces, for example, optical.
MAC Address Table Size... To select a switch, it is important to calculate in advance the size of the table you need, preferably taking into account the future expansion of the network. If there are not enough records in the table, the switch will overwrite the new ones, and this will slow down the data transfer.
Form Factor... The switches are available in two types of chassis: desktop / wall mount and rack mount. In the latter case, the standard device size is 19-inches. The special rack mount ears can be detachable.
Choosing a switch with the functions we need to work with traffic
Flow control ( Flow control, IEEE 802.3x protocol). Provides for the negotiation of send and receive data between the sending device and the switch at high loads, in order to avoid packet loss. The function is supported by almost every switch.
Jumbo frame- increased packages. It is used for speeds from 1 Gbit / s and above, allows you to speed up data transfer by reducing the number of packets and the time for their processing. There is a function in almost every switch.
Full-duplex and Half-duplex modes... Almost all modern switches support auto-negotiation between half-duplex and full-duplex (data transmission in one direction only, data transmission in both directions at the same time) to avoid network problems.
Traffic prioritization (IEEE 802.1p standard)- the device is able to identify more important packets (for example, VoIP) and send them first. When choosing a switch for a network where a significant part of the traffic will be audio or video, you should pay attention to this function.
Support VLAN(standard IEEE 802.1q).
VLAN is a convenient tool for delimiting individual areas: the internal network of an enterprise and a public network for customers, various departments, etc.
Mirroring (traffic duplication) can be used to ensure security within the network, to monitor or verify the performance of network equipment. For example, all incoming information is sent to one port for verification or recording by certain software.
Port forwarding... You may need this function to deploy a server with Internet access, or for online games.
Loop protection - STP and LBD functions... Especially important when choosing unmanaged switches. It is almost impossible to detect the formed loop in them - a looped section of the network, the cause of many glitches and freezes. LoopBack Detection automatically blocks the port on which the loop has occurred. The STP protocol (IEEE 802.1d) and its more advanced descendants - IEEE 802.1w, IEEE 802.1s - act a little differently, optimizing the network for a tree structure. Initially, the structure provides for spare, looped branches. By default, they are disabled, and the switch starts them only when there is a disconnect on some primary line.
Link Aggregation (IEEE 802.3ad)... Increases bandwidth by combining multiple physical ports into one logical port. The maximum bandwidth for the standard is 8 Gbps.
Stacking... Each vendor uses their own stacking designs, but in general terms, this feature refers to the virtual aggregation of multiple switches into a single logical device. The goal of stacking is to get more ports than is possible using a physical switch.
Switch functions for monitoring and troubleshooting
Many switches detect a cable connection fault, usually when the device is turned on, as well as the type of fault - wire breakage, short circuit, etc. For example, D-Link has special indicators on the case:
Virus Traffic Protection (Safeguard Engine)... The technique allows to increase the stability of work and protect the central processor from overloading by the "garbage" traffic of virus programs.
Power supply functions
Energy saving.How to choose a switch that will save you energy? Pay attentione for the availability of energy saving functions. Some manufacturers, such as D-Link, produce switches with adjustable power consumption. For example, a smart switch monitors devices connected to it, and if any of them is not working at the moment, the corresponding port is put into "sleep mode".
Power over Ethernet (PoE, IEEE 802.af standard)... A switch using this technology can power the devices connected to it over the twisted pair.
Built-in lightning protection... A very useful function, but remember that such switches must be grounded, otherwise the protection will not work.
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