Grade10_The principles of computer networks_coursePlan

Aims:
10.6.1.1 describe the purpose of network components (nodes, routers, switches);

When transmitting data in any medium, the signal attenuation occurs, which
leads to limiting the length of the network distance. To overcome this limitation and expand the network, install special expansion devices, specialized subscribers (nodes) of the network, these include repeaters, bridges, routers (router) and gateways.
These devices are used to unite several heterogeneous networks into a single network with different exchange protocols, in particular, with one-off packet formats, different coding methods, and different transmission speeds.
As a result of their use, a complex and heterogeneous network containing the most diverse 2 segments, from the user's point of view, looks like a regular network. The part of the network, which does not include the extension device, is called a network segment

Network switch or switch (jarg. From the English. Switch - switch) - a device designed to connect several nodes of a computer network within one segment. Unlike a hub that propagates traffic from one connected device to all others, the switch only transmits data directly to the recipient, with the exception of broadcast traffic (to the MAC address FF: FF: FF: FF: FF: FF) to all network nodes. This improves the performance and security of the network, eliminating the remaining network segments from the need (and ability) to process data that was not intended for them.

The switch operates at the data link layer of the OSI model, and therefore, in the general case, it can only combine nodes on the same network by their MAC addresses. Switches have been developed using bridge technology and are often viewed as multiport bridges.

Для соединения нескольких сетей на основе сетевого уровня служат маршрутизаторы.

The switchboard stores in memory a switch table (stored in the associative memory), which indicates the corresponding MAC address of the node to the switch port. When the switch is turned on, this table is empty, and it works in the learning mode. In this mode, the data arriving at any port is transmitted to all other ports of the switch. In this case, the switch analyzes frames (frames) and, having determined the MAC address of the sending host, enters it into a table. Subsequently, if one of the switch ports receives a frame destined for a host whose MAC address is already in the table, this frame will be transmitted only through the port specified in the table.
If the destination host's MAC address is not associated with any switch port, then the frame will be sent to all ports.
Over time, the switch builds a complete table for all of its ports, and as a result, traffic is localized.
.

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

Intermediate storage (Store and Forward). The switch reads all the information in the frame, checks it for errors, selects the switching port and then sends the frame to it.
Cut-through. The switch reads only the destination address in the frame and then performs the switching. This mode reduces transmission delays, but there is no error detection method.
Fractional (fragment-free) or hybrid. This mode is a modification of end-to-end mode. The transmission is carried out after filtering fragments of collisions (a frame with a size of 64 bytes is processed using the store-and-forward technology, the rest using the cut-through technology).

A router is a network device that, based on information about the network topology and certain rules, makes decisions about forwarding network layer packets (level 3 of the OSI model) between different network segments.
Works at a higher level than the switch and network bridge.

Typically, the router uses the destination address specified in the data packets, and the routing table determines the path to which the data should be sent. If there is no described route in the routing table for the address, the packet is dropped.
There are other ways to determine the packet forwarding route, for example, when the sender's address is used, the upper protocols used, and other information contained in the packet headers of the network layer. Often, routers can translate addresses of the sender and recipient, filter the transit data flow based on certain rules in order to restrict access, encrypt / decrypt transmitted data, etc.

The routing table contains information on the basis of which the router decides on the further forwarding of packets. The table consists of a number of records — routes, each of which contains the recipient’s network address, the address of the next node to which packets should be sent, and a certain weight of the record — a metric. Table entry metrics play a role in calculating the shortest routes to different recipients. Depending on the router model and routing protocols used, the table may contain some additional service information.
For example:
192.168.64.0/16 [110/49] via 192.168.1.2, 00:34:34, FastEthernet0 / 0.1
Where
    192.168.64.0/16 - destination network,
    110 / - administrative distance
    / 49 - route metric,
    192.168.1.2 - the address of the next router to which the packets for the network 192.168.64.0/16 should be transmitted,
    00:34:34 - the time during which this route was known,
    FastEthernet0 / 0.1 - router interface through which you can reach the “neighbor” 192.168.1.2.

Routers help reduce network load by splitting into collision domains1 or broadcast domains2, as well as packet filtering.
They are mainly used to connect different types of networks, often incompatible in architecture and protocols, for example, to connect local Ethernet networks and WAN connections. Often, a router is used to provide access from a local network to the global Internet, carrying out the functions of address translation and a firewall.
As a router can act as a specialized (hardware) device, and a normal computer that performs the functions of a router. There are several software packages (in most cases, based on the Linux kernel) with which you can turn your PC into a high-performance and multi-functional router, such as Quagga.

[1]Доме́н колли́зий — сегмент сети, имеющий общий физический уровень, в котором доступ к среде передачи может получать только один абонент одновременно. Задержка распространения сигнала между станциями, либо одновременное начало передачи вызывает возникновение коллизий, которые требуют специальной обработки и снижают производительность сети.
[2]Широковеща́тельный доме́н (сегмент) — логический участок компьютерной сети, в котором каждое устройство может передавать данные любому другому устройству непосредственно, без использования маршрутизатора. Устройства, ограничивающие широковещательный домен — маршрутизаторы, работающие на третьем, сетевом уровне модели OSI, и коммутаторы на втором уровне модели OSI, поддерживающие технологию VLAN. Устройства первого уровня — концентраторы и повторители, а также коммутаторы без поддержки VLAN широковещательный домен не ограничивают.