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The principle of operation of a network concentrator (hub)

Or network hub- this is a device for connecting several Ethernet devices to each other; in the future, the devices operate as one network segment.

Has several input/output ports. The signal is applied to one of the input ports and output to all others except the input port. This device operates on physical level OSI network model. A network hub is a type of repeater that participates in collision detection (overflow), resuming data transmission to the port after a random time interval if a collision is detected. IN Lately hubs have become less relevant due to the high popularity of network switches.

The network hub is simple device. It does not have a traffic control function; each data packet that arrives at a port is automatically relayed to all others. The device does not track the transmission source and destination. Although, if you wish, you can use a special software, which controls and records the flow of transmitted information in its database. This information can be viewed in text form, for example using Word. A download Word 2003 for free It's easy on the Internet. This monitoring of data movement through a network hub is very convenient for system administrators.

Characteristics of a network concentrator (hub)

• Number of ports: 2-48. 4,8,16 ports are often used.
• Data transfer rate. 10 Mbit/s or 100 Mbit/s.
• Availability different interfaces connections (optical, coaxial)

Advantages and disadvantages of network hub(s)

Advantages

• Low cost of the device

Flaws

• As connected devices increase, the throughput decreases, which is divided among all involved devices.
• Since the ports in network hub are not isolated, then the entire network segment operates at the speed supported by the slowest device.
• Low security.

A little about network structuring

To build the simplest single-segment network, it is enough to have network adapters and a cable of the correct type. But even in this case, additional devices are often used - signal repeaters, which make it possible to overcome the limitations on maximum length cable segment.

Main function repeater(repeater), as its name suggests, repeats signals arriving at one of its ports on all other ports (Ethernet) or on the next port in the logical ring ( Token Ring, FDDI) synchronously with incoming signals. Repeater improves electrical characteristics signals and their synchronization, and due to this it becomes possible to increase the total cable length between the most remote stations in the network.

A multiport repeater is often called hub(hub), which reflects the fact that this device implements not only the signal repetition function, but also concentrates in one central device functions of connecting computers into a network. In almost all modern network standards, a hub is necessary element networks connecting individual computers into a network.

The pieces of cable connecting two computers or any two other network devices are called physical segments. Thus, hubs and repeaters, which are used to add new physical segments, are a means of physically structuring the network.

Hubs form a common data transmission medium from individual physical cable sections - logical segment. A logical segment is also called a collision domain, since when attempting to simultaneously transmit data from any two computers in this segment, even if they belong to different physical segments, the transmission medium is blocked. It should be especially emphasized that no matter how complex the structure the hubs form, for example, through a hierarchical connection, all computers connected to them form a single logical segment in which any pair of interacting computers completely blocks the ability to exchange data for other computers.

What is a hub?

hub hub (wheels).

English-Russian dictionary

Hub is a multiport network repeater with auto-segmentation. All hub ports are equal. Having received a signal from one of the stations connected to it, the hub broadcasts it to all its active ports. In this case, if a fault is detected on any of the ports, then this port is automatically disabled (segmented), and after it is eliminated, it becomes active again. Auto segmentation necessary to improve network reliability. Collision processing and ongoing monitoring of the state of communication channels is usually carried out by the concentrator itself. Hubs can be used as standalone devices or connect to each other, thereby increasing the size of the network and creating more complex topologies. In addition, it is possible to connect them with a backbone cable into a bus topology. Since the logic of access to the shared medium significantly depends on the technology, each type of technology produces its own models - Ethernet hubs, Token Ring hubs, FDDI hubs, VG-AnyLAN hubs.

A hub is a general name for devices that form a shared environment, regardless of the type of protocol being implemented. For a specific protocol, sometimes a narrow name for this device is used, which more accurately reflects its functions, or is used due to tradition, for example, as the name MAU for Token Ring concentrators.

Purpose of hubs- combining individual workstations into a work group within a local network. For working group The following features are characteristic: a certain territorial concentration; a team of working group users solves similar problems, uses the same type of software and common information bases; within the working group there are common requirements for ensuring safety and reliability, the same impact occurs external sources disturbances (climatic, electromagnetic, etc.); high-performance peripherals are shared; usually contain their own local servers, often geographically located on the territory of the working group.

Hubs and OSI model

Hubs work on physical level(Level 1 basic reference model OSI). Therefore, they are not sensitive to upper-layer protocols. The result of this is the possibility sharing various operating systems(Novell NetWare, SCO UNIX, EtherTalk, LAN Manager, etc., compatible with Ethernet or IEEE 802.3 networks). There is, however, a certain “pressure” on the network owner when using network management programs: management programs, as a rule, use the IP protocol to communicate with SNMP equipment. Therefore, in terms of network management, you have to use only these protocols and, accordingly, operating shells at network management stations. But this is not a very serious pressure, because the IP protocol is probably the most popular.

General properties of concentrators

Most concentrators have the following characteristic performance features:

• equipped LED indicators, indicating the status of ports (Port Status), presence of collisions (Collisions), transmission channel activity (Activity), presence of fault (Fault) and presence of power (Power), which provides quick monitoring of the status of the entire hub and diagnosis of faults
• When the power supply is turned on, a self-test procedure is performed, and during operation, a self-diagnosis function is performed.
• have standard size width - 19 inches;
• provide auto-segmentation of ports to isolate faulty ports and improve network integrity
• Detects polarity error when using twisted pair cable and automatically switches polarity to correct wiring error
• support configurations using multiple hubs connected to each other or via special cables and stack ports, either a thin coaxial backbone connected between BNC ports, or via fiber optic or thick coaxial cable connected via appropriate transceivers to the AUI port, or via UTP cables connected between the ports of the hubs
• support voice and data communications over the same cable harness
• transparent to software network operating system
• can be installed and put into operation within a few minutes

Types of concentrators

Hubs entry level - five-, eight-, less often twelve-, sixteen-port hubs. They often have an additional BNC port, less often an AUI port. It does not provide management capabilities either through the console port (due to its absence) or over the network (due to the absence of an SNMP module). They are a simple and cheap solution for organizing a small work group.

Mid-range hubs- twelve-, sixteen-, twenty-four-port hubs. They have a console port, often additional BNC and AUI ports. This type of hub provides out-of-band network management capabilities through an RS-232 console port under the control of some standard terminal program, which makes it possible to configure other ports and read hub statistics. This type of hubs is positioned for building networks in the range from small to medium-sized, which will further develop and require the introduction program control.

SNMP-managed concentrators- twelve-, sixteen-, twenty-four- and eight-port hubs. They are distinguished not only by the presence of an RS-232 console port for management, but also by the ability to manage and collect statistics over the network using the SNMP/IP or IPX protocols. The owner of such a hub has access to the following collection of statistics on network nodes (hubs), its primary processing and analysis: the main sources of messages (top talkers), the most active users (heavy users), sources of errors and communication pairs are identified. It is advisable to use these types of hubs for building local networks in the range of medium and higher, which will certainly develop. These networks always require software network management, including remote control.

BNC hubs or ThinLAN hubs- multiport repeaters for thin coaxial cables used in 10Base2 networks. They include BNC ports and, as a rule, one AUI port, and often support SNMP protocols. They, like 10Base-T hubs, segment ports (disabling not just one station, but subscribers of the entire physical segment) and broadcast incoming packets to all ports. Each BNC port is subject to the same restrictions as a fragment of a 10Base-2 standard network: the operation of thin coaxial cable segments up to 185 meters long per port is supported, up to 30 network connections per segment, including “empty T-connectors”; If a cable segment fails, that segment will be disabled, but the rest of the hub will continue to function. Scope of application of concentrators of this type- modernization of old 10Base2 standard networks in order to increase their reliability, modernization of networks that have reached restrictions on the use of repeaters and do not require frequent changes.

10/100Hubs have appeared recently. If you just read advertisements about them, you can be “ambushed.” The fact is that hubs do not know how to buffer packets, and therefore cannot negotiate different speeds. Therefore, if at least one 10Base-T station is connected to such a hub, then all ports will operate at its speed. Rumor has it that there are already hubs that support two speeds simultaneously. Perhaps in this case, the manufacturer uses the word “hub” to refer to some kind of intermediate device (something in between a hub and a switch), such as MicroLAN from Cabletron Systems.

Additional functions

Redundant link. Mid-range and SNMP-managed hubs support one redundant link per hub to create a back-up link between any two hubs. This ensures network fault tolerance at the hardware level. The redundant link is a separate cable mounted between two hubs. Using the hub's console port, you simply need to configure the primary link and backup link for one of the hubs. The backup communication channel is automatically released if the main communication channel of two concentrators fails. Despite what the hub can control only one backup link, it can be at the remote end of one backup link and at the controlling end of a backup link to another hub. Once the fault on the primary cable segment is corrected, the primary link will not automatically resume operation. To resume main communication, you will have to use the hub console or press Reset button on his body.

"Connective bit" for concentrators, it is a periodic pulse lasting 100 nanoseconds, sent every 16 milliseconds. It does not affect network traffic. The communication bit is sent during periods when the network is not transmitting data. This function monitors the safety of the UTP channel. This function should be used in all possible cases and blocked only when a device that does not support it is connected to the hub port, for example, equipment like HP StarLAN 10.

Ensuring secrecy in networks built using hubs, a rather thankless task, since a hub, by definition, is a broadcast device. But if necessary, the following tools may be available to the network administrator: blocking unused ports (by distorting the data field in frames repeated on ports that do not contain a computer with the destination address), setting a password for the console port, setting information encryption on each of the ports (some models have this opportunity).

Multifunctional modular hubs

When building a complex network, all types of communication devices can be useful: hubs, bridges, switches, and routers (network adapters are excluded from this list because they are always needed). Most often, a single communications device performs only one primary function, being either a repeater, a bridge, a switch, or a router. But this is not always convenient, since in some cases it is more rational to have a multifunctional device in one case that can combine these basic functions and thus allows the network developer to use it more flexibly.

Ideally, one can imagine a universal communication device that has a sufficient number of ports for connecting network adapters, which are combined into groups with programmable functions for interrelating with each other (according to the repeater, switch or router algorithm). However, it is known that any universalization always harms the quality of performance of narrow special functions and, perhaps therefore, on modern level technology development is completely universal device has not yet appeared, although separate combinations of functions in one device are sometimes performed.

Thus, routers can often act as bridges, depending on how their software is configured by the administrator. But the repeater functions require high performance, which can only be achieved at a purely hardware level. Therefore, repeater functions are not combined with bridge or router functions.

A different approach can be used to combine functions. IN special devices - modular hubs - individual components, performing one of the three described main functions, are implemented in the form of modules installed in general building. In this case, intermodular connections are not organized externally, as is done when modules are individual devices, but via the internal buses of a single device.

Modular multifunctional devices are often called hubs, emphasizing their centralizing role in the network. In this case, the term “hub” is used not as a kind of synonym for the term “repeater”, but in a broader sense. It is necessary to understand well in each specific case functional purpose individual modules of such a hub. Depending on the configuration, a modular multifunctional hub can combine the functions of a repeater (of various technologies), a bridge, a switch, and a router, or it can perform only one of them.

Switch or hub?

When building small networks that make up the lower level of the hierarchy corporate network, the question of using a particular communication device comes down to the question of choosing between a hub or a switch.

There are several factors to consider when answering this question. Of course, it is of no small importance cost per port, which you need to pay when choosing a device. For technical reasons, it is first necessary to take into account the existing traffic distribution between network nodes. In addition, it is necessary to take into account the prospects for the development of the network: will multimedia applications be used soon, will it be modernized? computer base. If yes, then we need to ensure reserves for bandwidth used communication equipment. The use of Intranet technology also leads to an increase in the volume of traffic circulating on the network, and this must also be taken into account when choosing a device.

When choosing a device type - hub or switch - you also need to determine and protocol type which its ports (or protocols, if we're talking about about the switch, since each port can support a different protocol).

Choosing a communication device for a network with a dedicated server is quite complicated. To make a final decision you need to take into account network development prospects in relation to movement towards balanced traffic. If interaction between workstations or a second server may soon appear on the network, then the choice must be made in favor of a switch that can support additional traffic without prejudice to the main one.

Another factor that can play in favor of the switch is distances- the use of switches does not limit the maximum network diameter to 2500 m or 210 m, which determine the size of the collision domain when using Ethernet and Fast Ethernet hubs.

Features of national governance

How do they manage to steal in Russia when there is no money anywhere, nothing to steal? Everything is very simple: in the West they steal from profits, but in our country they steal from expenses.

Sad joke

Russian network administrators have particularly warm feelings about hubs, and here's why. Let me list once again the main criteria that it is advisable to follow when choosing a communication device:

· Price

· Traffic distribution

Protocol type

· Network development prospects

· Distance factor

And here’s how (I’m exaggerating, of course) the same list looks in the eyes of a typical Russian manager who makes a decision to purchase equipment for small network:

· Price

They turn a blind eye to traffic distribution, the type of protocol and geometric configuration of the network are chosen based on which equipment costs less, and it is not customary to think about development prospects at all. As a result, equipment is purchased that is cheaper “here and now,” “as long as it works.” Naturally, the most popular network technology is Thin Ethernet, the most popular server software (until recently) is Novell NetWare, and without any additional devices They try to do their best as long as the entire network fits on one physical segment.

So how does a typical manager answer the question “hub or switch”? Whatever is cheaper! Of course, a hub, and often with such a number of ports that only “end to end” is enough.

This is such a glorious national tradition.

No, it’s still time to change traditions. It's time system administrator explain to your boss that saving now will result in even greater expenses in a couple of years.

In no way did I want to offend any of the leaders. It's nice to know that there are exceptions to the rules, and, fortunately, there are more and more such exceptions over time.

Today it is impossible to imagine the office of even the smallest company without a local network, which means that in the distribution cabinet of each office there is a main network device - a hub (Hub) or a switch (Switch).

The operating principles of a hub and a switch are significantly different, and choosing one over the other can have a significant impact on network performance.

How does the hub behave?

The logic of the hub is as follows: when the hub receives an electrical signal, it transmits it to all ports except the one from which the signal was received. This means that a data frame received from one computer will be sent to all other computers connected to the network.

Obviously, in a local network with a hub, each computer receives many frames, but only some of them are intended for it. The network interface board of each computer must receive all frames and process each of them: read the recipient's address in the frame header, compare it with its own MAC address. If the addresses do not match, network card ignores the frame. If the addresses match, it is considered that the frame has reached its destination and is processed further. Those. the computer received information intended specifically for it.

What happens on the network due to the fault of the hub?

1. Traffic is increasing.
2. There are a lot of frame accidents that happen.

This means that network performance decreases, and the percentage of data lost while passing through the network increases.

Is it possible to avoid data loss?

It is possible if the hub is replaced with a switch. The switch receives a frame with data, reads the recipient's MAC address from its header, and sends this frame only to the port that leads to the recipient. This device accepts smart solution! Looks the same twisted pair for data transmission and another one for receiving, the same network devices, but the result is different. The network is orderly and calm, there is no excess of frames moving uselessly in the direction of adapters that will surely reject them.

There are, of course, situations when the switch receives several frames simultaneously for one recipient. In this case, the switch also behaves like an intelligent device: it sends one frame to the recipient immediately, and places the rest in a buffer, from where they will go to their destination in turn, after a certain period of time. Thus, the switch prevents the occurrence of emergency situations and, consequently, the loss of data on the network.

And if data loss occurs, it is only due to natural interference.

So is the switch better?

The switch, of course, wins in comparison with the hub. And if your network is large enough, it would be wiser to purchase it.

However, in a small network with several computers, you most likely will not feel the difference in the operation of a hub or switch. But you will feel the difference in price, so for a small network it is quite justified to purchase a hub.

USB technology, which was invented to connect computer and telecommunication devices, is now the main means of connecting many gadgets. Their number is simply surprising - these are keyboards, mice, modems, coolers, external hard disks, printers, flash drives, even coffee makers and lamps. And since all these devices need to be connected to a computer, there are currently simply not enough USB ports.

Decide this problem possible in two ways. The easiest way is to connect only those devices that are needed this moment, and disconnect unused devices, thereby freeing up USB ports. And the second way is to purchase an original device called a USB concentrate (USB hub).

The USB hub is small device, which has several USB ports. It connects to one of the computer's USB ports (thus taking up only one USB connector), and makes it possible to use several USB devices. Thus, a USB hub increases the number USB connectors on your computer, reduces their wear and tear, and also makes it easier to use multiple devices.

Types of USB hubs

There are four types of USB hubs. The first one is USB card PCI, which connects to the PCI slot on motherboard. To do this you will have to open system unit, and if you don’t understand this, then it’s better not to use this type of USB hub.

The second type is a non-powered USB hub. This simple device connects to one of your computer's external USB ports. After this, you can connect any other devices to it. These USB hubs are very compact and are great for both computers and laptops. But they have a small disadvantage. Some USB devices (printer, digital camera, scanner, etc.) require power supply, and this type the hub will not be able to provide them with the required amount of electricity, especially if you connect several devices at once.

The third type is a powered USB hub. It is also very compact and plugs into an external USB port on your computer. In addition, such a USB hub can be plugged directly into an outlet. This makes it possible to connect any types of USB devices to it.

And the fourth type is computer card USB. If you use a laptop for work and also need to constantly move with it, then an excellent alternative The USB hub will have just such a USB card. It connects to the USB connector on the side of the laptop and allows you to connect two additional devices.

Hub - a central node for information exchange between several network end stations. The hub operates at the physical layer network model OSI, repeats a signal arriving on one port to all active ports. If a signal arrives on two or more ports at the same time, a collision occurs and the transmitted data frames are lost.

Switch - transmits packets between all pairs of ports using the bridge algorithm. Unlike a hub, which distributes traffic from one connected device to all others, a switch transmits data only directly to the recipient. The switch operates at the data link layer of the OSI model.

Operating principle of the switch: The switch stores a table in memory that indicates the mapping of the host MAC address to the switch port. When the switch is turned on, this table is empty and the switch is in learning mode. In this mode, data arriving on any port is transmitted to all other ports of the switch. In this case, the switch analyzes the frames and, having determined the MAC address of the sending host, enters it into the table. Subsequently, if one of the switch ports receives a frame intended for a host whose MAC address is already in the table, then this frame will be transmitted only through the port specified in the table. If the MAC address of the recipient host is not yet known, then the frame will be duplicated on all interfaces. Over time, the switch builds full table for all its ports, and as a result the traffic is localized

Switching modes.

There are three switching methods. Each of them is a combination of parameters such as latency and transmission reliability.

With intermediate storage. The switch reads all the information in the frame, checks it for errors, selects a switch port, and then sends the frame to it.

Through. The switch reads only the destination address in the frame and then performs the switching. This mode reduces transmission delays, but does not have an error detection method.

Fragmentless or hybrid. This mode is a modification of the pass-through mode. The transmission is carried out after filtering collision fragments.

Features of the technical implementation of switches.

switch matrix; The main and most quick way interaction between port processors. The port processor input blocks, based on a scan of the switch's address table, determine the output port number from the destination address. They add this information to the bytes of the original frame in the form of a special label - a tag.

shared memory; The input blocks of the port processors are connected to the switched input of the shared memory, and the output blocks of the same processors are connected to the switched output of this memory. The switching of shared memory input and output is controlled by the output port queue manager. In shared memory, the manager organizes several data queues, one for each output port. Processor input blocks send requests to the port manager to write data to the queue of the port that corresponds to the destination address of the packet. The manager, in turn, connects the memory input to one of the processor input blocks, and it rewrites part of the frame data into the queue of a specific output port. As the queues fill, the manager also alternately connects the output of the shared memory to the output blocks of the port processors, and the data from the queue is rewritten to the output buffer of the processor.

common bus. Shared bus switches use a high-speed time-sharing bus to communicate between port processors. The processor input block places a tag in a cell carried on the bus, which indicates the destination port number. Each port processor output block contains a tag filter that selects tags intended for this port. The bus, like the switching matrix, cannot perform intermediate buffering, but since the frame data is divided into small cells, there is no delay in the initial wait for the output port to be available in such a scheme.

Design of switches.

standalone switches with a fixed number of ports;

chassis-based modular switches;

switches with a fixed number of ports, assembled into a stack.

Managed SwitchesEthernet. Switches are managed based on the SNMP (Simple Network Management Protocol) and RMON (Remote Monitoring) protocols. SNMP protocol is part of the TCP/IP protocol stack and is widely used to obtain information from a switch about its status, performance, and other characteristics, which are stored in the switch database. The RMON protocol defines the ability to remotely monitor and manage the switch.

RMON allows you to manage and monitor the status of the switch from a remote computer with the ability to transfer the required data over the network. In addition, additional error counters, more flexible statistics analysis tools, filtering tools, etc. have been added to the RMON protocol.

Managed switches also have additional functions, the most important of which are: 1. traffic filtering; 2. priority processing of frames; 3. support for Spanning Tree Protocol (STP); 4. support for trunked port aggregation; 5. support for virtual VLANs.

Traffic filtering allows you to create custom filters that limit the access of predefined groups of users to certain services networks. In fact, traffic filtering is a service that increases the level of network security.

Priority frame processing implies the ability to process incoming frames not on a First Input First Output (FIFO) basis, where each frame is processed in accordance with its arrival queue, but in accordance with a specified priority.

Support for the Spanning Tree Protocol, that is, the spanning tree algorithm, determines the correct operation of the switch in the case when there are several logical or physical routes between the end nodes of the network, which include switches. Such duplicate paths can arise accidentally, due to errors in network installation, or they can be laid specifically to increase the fault tolerance of the network. The essence of the algorithm is to determine the optimal route and block or reserve all others

Support for port trunking allows you to create high-speed communication channels by combining several physical channels into one logical one, which can be used to connect switches with each other or a switch with a server.

Support for virtual networks (Virtual LAN, VLAN) allows you to create local networks isolated from each other using the switch.

SpanningTree.

Spanning tree protocol.

Bridges and switches that support the STA algorithm automatically create an active tree configuration of links (that is, a connected configuration without loops), adaptively finding it through the exchange of service packets.

The network is determined root bridge(root bridge), from which the tree is built. For each bridge it is determined root port(root port) is the port that has the shortest distance of all ports on a given bridge to the root bridge (more precisely, to any of the ports of the root bridge).

Distance to root(root path cost) is defined as the total conditional time for data transfer from the port of a given bridge to the port of the root bridge. Conditional segment time(designated cost) is calculated as the time spent transmitting one bit of information in 10 nanosecond units between ports directly connected along a network segment. So, for an Ethernet segment this time is equal to 10 conventional units, and for a Token Ring segment of 16 Mb/s - 6.25.

For each logical network segment, a so-called designated bridge(designated bridge), one of the ports of which will receive packets from the segment and transmit them in the direction of the root bridge through the root port of this bridge, and also receive packets for this segment arriving at the root port from the root bridge. This port is called designated port(designated port). The designated port on a segment has the shortest distance to the root bridge among all the ports connected to that segment. A segment can only have one designated port. For a root bridge, all ports are designated, and their distance to the root is set to zero. The root bridge does not have a root port.

In order for bridges to identify themselves and their near and far neighbors on the network, each bridge supporting an STA has a unique identifier. This identifier consists of two parts. The low part is the bridge MAC address, which is 6 bytes long. The high part, which is 2 bytes long, is the priority of this bridge, and it can be changed by the network administrator at his discretion.

The bridge ID plays a determining role in selecting the root bridge. Priority takes precedence in this choice - the bridge with the lowest identifier value is selected as the root bridge, and since the priority field is in the most significant bits, its value suppresses the value of the MAC address. If the administrator assigned equal priority to all bridges (that is, did not want to influence the choice of the root bridge), then the bridge with the lowest MAC address will be selected as the root bridge.

Ports within each bridge also have their own identifiers. The port identifier consists of 2 bytes, the first of which (major) can be changed by the administrator and is the priority of the port, and the second is the port sequence number for this bridge (port numbers begin with one). The port identifier is used when selecting the root and designated port of the bridge - if several ports have the same distance to the root, then the port with the smaller identifier is selected. Similar to the bridge ID case, the port priority can be set by the administrator to give a given port priority over others.

VLAN. A virtual network (Virtual LAN, VLAN) is a group of network nodes whose traffic, including broadcast traffic, is completely isolated at the link level from other network nodes. This means that frames cannot be transmitted between different virtual segments based on a link-layer address, regardless of the type of address - unique, multicast, or broadcast. The purpose of virtual network technology is to facilitate the process of creating independent networks, which must then communicate using network layer protocols

Types of virtual networks

There are several main ways to build virtual networks:

Grouping of ports.

Grouping of MAC addresses.

Use of labels in the frame's optional field - proprietary protocols and IEEE 802.1 Q specifications.

VLAN based on port grouping.

Devices communicate in virtual networks based on the switch ports to which they are physically connected. That is, each switch port is included in one or more virtual networks. The advantages of this type of virtual networks include high level security and ease of setup. The disadvantages include the static nature of this type of virtual networks. That is, when connecting a computer to a different switch port, you must change the VLAN settings each time.

VLAN based on grouping of MAC addresses.

This type of virtual network groups devices based on their MAC addresses. To gain access to a virtual network, the device must have a MAC address that is contained in the list of addresses for this virtual network. Among other things, a distinctive feature of this type of virtual networks is that they limit only broadcast traffic. This is where their name comes from – broadcast domains based on MAC addresses. Theoretically, one MAC address can be a member of several broadcast domains; in practice, this possibility is determined by the functionality of a particular switch model.

MAC address-based broadcast domains allow a station to be physically moved while still allowing it to remain in the same broadcast domain without any changes to configuration settings.

VLAN based on tagged frames (IEEE 802.1Q).

Unlike the previous two types of virtual networks, VLANs based on tagged frames can be implemented on two or more switches. A token is inserted into the header of each Ethernet frame that identifies the computer's membership in a particular VLAN.

Markers with VLAN number in virtual networks 802.1Q can be added:

explicitly, if network cards support the IEEE 802.1Q standard, and the corresponding options are enabled on these cards, then outgoing Ethernet frames these cards will contain identification markers;

implicitly, if the network adapters connected to this network do not support the IEEE 802.1Q standard, then adding tokens is done on the switch based on port grouping.