What is a lan switch. Selecting a Suitable LAN Device. How does the switch work?

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

Each LAN has a router that 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 a router connects to a different network and routes packets between networks. Routers can split broadcast domains 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. Usually these are UTP cable connections, but modules can be added in order to use fiber optics... Depending on the series or model of routers, they can have several types of interfaces for WAN and LAN cable connections.

Intranet devices

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

Concentrator

The concentrator receives the signal, regenerates it and sends it to all ports. Using hubs creates a logical bus. This means the LAN is using the media in multi-access mode. Ports use a bandwidth sharing approach, which often results in degraded LAN performance due to collisions and recovery. Although it is possible to connect multiple hubs, 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 limited finances.

Switch

The switch accepts the frame and regenerates every bit of the frame to the appropriate destination port. This device is used to segment the network into multiple collision domains. Unlike a hub, a switch reduces LAN collisions. 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 increase 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 the switch is more expensive than a hub, its improved performance and reliability make it cost effective.

There are a variety of feature-rich switches available that allow you to connect multiple computers in a typical enterprise LAN setup.

Construction issues local area networks appear 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 task - 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 entirely depends 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 specified by the sender, relieving the network of 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 the 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.

Conclusions site

1. Hub - hub, switch - switch.
2. The hub device is the simplest, the switch is more “intelligent”.
3. The hub transmits the signal to all clients of the network, the switch - only to the addressee.
4. The performance of a network organized through a switch is higher.
5. The switch provides a higher level of data transmission security.
6. The hub works at the physical layer of the OSI network model, the switch works at the channel one.
7. The switch needs to be configured correctly network cards clients of the network.

This chapter introduces technologies at work in devices that are loosely named bridges and switches... Topics summarized here include general principles of channel devices, local and remote bridging, ATM and LAN switching. Subsequent chapters in Part 4, "Bridges and Switches," of this book deal with the specifics of these technologies in more detail.

What are Bridges and Switches?

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

Bridges became commercially available in the early 1980s. At the time of their introduction, bridges were connected and allowed the forwarding of packets between homogeneous networks. In more recent times, bridging between different networks has also been defined and standardized.

Several types of bridges have become important as internetworking devices. Transparent bridges are found primarily in the Ethernet environment, while source-route bridges appear primarily in a Token Ring environment. Translational Bridge provide transmission between formats and transit principles different types media (usually Token Ring and Ethernet). Finally, source-route transparent bridge combine transparent and pre-routed bridging algorithms to enable communication in mixed Ethernet / Token Ring environments.

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

Data Link Layer Overview

While bridges and switches share most of the features, there are some features that set these technologies apart. Switches are significantly faster because they switch in hardware, while bridges are software-switched and can also interconnect LANs with unequal bandwidth. For example, a switch can be used to connect local networks of 10- and 100-megabit Ethernet. Switches also support higher port densities than bridges. Some switches support cut-through switching, which reduces network latency and latency, while bridges only support store-and-forward switching. Finally, switches reduce collisions on network segments by providing dedicated bandwidth to each network segment.

Bridge types

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 are classified as They are designed to function 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 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. Such 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, network adapter, which 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, upper-layer protocols and all the data hidden behind the set name 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 secure.

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 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 his the main task- 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 be consistent with the other configuration in the network at all times.

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.

Switch one of critical devices used to build 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.

To begin with, let's look at the general block diagram in order to understand what place the switch occupies in the local network of the enterprise.

The picture above shows the most common structural scheme 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 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 a local network that manage data transfer on their own and do not have the ability to additional customization... 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... TO this level include 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 on 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.

Suppose the installation of a local network is made in the form of a ring to increase the system's fault tolerance. 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.Maximum speed determined IEEE standard 802.3ad 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 ownership different applications and make decisions to redirect 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 network board 1 Gbps 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 the local network there is a switch with 5 ports operating at a speed of 10/100 Mbit / s. V technical characteristics the switch matrix parameter 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 in the end check sum 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 mode commutation 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 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 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 decision allows you to reduce money costs for additional installation of supply lines.

The following PoE standards exist:

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 network cable without any approvals.

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 surveillance cameras, where 15.4 watts cannot be kept within. 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 for data transmission 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 to different lengths waves over one optical cable.

SFP modules are:

• SX - 850nm is used with multimode optical cable at 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 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 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 performs installation, commissioning and maintenance of local networks in Krasnodar and the South of Russia.