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Routing protocols in IP networks. Network Routing Determining the Information Path

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-2.jpg" alt="(!LANG:>IP Routing Protocol">!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-3.jpg" alt="(!LANG:>IP address l IPv 4 -address is a unique 32 bit sequence of binary digits,"> IP-адрес l IPv 4 -адрес - это уникальная 32 разрядная последовательность двоичных цифр, с помощью которой компьютер однозначно идентифицируется в IP сети. (на канальном уровне в роли таких же уникальных адресов компьютеров выступают МАС адреса сетевых адаптеров, невозможность совпадения которых контролируется изготовителями на стадии производства.)!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-4.jpg" alt="(!LANG:>IP version l version 4, or IPv 4 l version 6 (IPv6)"> Версии l версия 4 протокола IP, или IPv 4 l версия 6 (IPv 6), в которой IP адрес представляется в виде 128 битной последовательности двоичных цифр. ipv 6 install!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-5.jpg" alt="(!LANG:>Structure l For convenience of working with IP addresses, a 32-bit sequence is usually"> Структура l Для удобства работы с IP адресами 32 разрядную последовательность обычно разделяют на 4 части по 8 битов (на октеты) l каждый октет переводят в десятичное число и при записи разделяют эти числа точками. l в таком виде (это представление называется «десятичные числа с точками» , или, «dotted decimal notation») IP адреса занимают гораздо меньше места и намного легче запоминаются 192. 168. 5. 200 11000000 10101000 0000101 11001000!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-6.jpg" alt="(!LANG:>Subnet mask l The subnet mask is a 32-bit number consisting of going"> Маска подсети l Маска подсети - это 32 разрядное число, состоящее из идущих вначале единиц, а затем - нулей, например (в десятичном представлении) 255. 0 ИЛИ 255. 240. 0.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-7.jpg" alt="(!LANG:>Subnet mask l The subnet mask plays an extremely important role in IP addressing and"> Маска подсети l Маска подсети играет исключительно важную роль в IP адресации и маршрутизации l сеть ARPANet строилась как набор соединенных друг с другом гетерогенных сетей. Для правильного взаимодействия в такой сложной сети каждый участник должен уметь определять, какие IP адреса принадлежат его !} local network, and which ones - to remote networks. l here the subnet mask is used, with the help of which any IP address is divided into two parts: the network identifier (Net ID) and the host identifier (Host ID). l such a division is very simple: where there are ones in the subnet mask, there is a network identifier, and where there are zeros, there is a host identifier. For example, in the IP address 192. 168. 5. 200, when using a subnet mask of 255. 0, the network ID will be the number 192. 168. 5. 0, and the host ID will be the number 200. It is worth changing the subnet mask to the number 255. 0. 0 , as well as the host ID and the network ID will change to 192.168.0.0 and 5.200, respectively, and from this, otherwise the computer will behave when sending IP packets.

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-8.jpg" alt="(!LANG:>Rules for assigning network and host IP addresses can only contain"> Правила назначения IP-адресов сетей и узлов 1. идентификатор сети не может содержать только двоичные нули или только единицы. Например, адрес 0. 0 не может являться идентификатором сети; 2. идентификатор узла также не может содержать только двоичные нули или только единицы - такие адреса зарезервированы для специальных целей l все нули в идентификаторе узла означают, что этот адрес является адресом сети. Например, 192. 168. 5. 0 является правильным адресом сети при использовании маски 255. 0 и его нельзя использовать для адресации компьютеров, l все единицы в идентификаторе узла означают, что этот адрес является адресом широковещания для данной сети. Например, 192. 168. 5. 255 является адресом широковещания в сети 192. 168. 5. 0 при использовании маски 255. 0 и его нельзя использовать для адресации компьютеров!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-9.jpg" alt="(!LANG:>Rules for assigning network and host IP addresses l host identifier within one and"> Правила назначения IP-адресов сетей и узлов l идентификатор узла в пределах одной и той же подсети должен быть уникальным; l диапазон адресов от 127. 0. 0. 1 до 127. 255. 254 нельзя использовать в качестве IP адресов компьютеров. Вся сеть 127. 0. 0. 0 по маске 255. 0. 0. 0 зарезервирована под так называемый «адрес заглушки» (loopback), используемый в IP для обращения компьютера к самому себе. PING 127. 12. 34. 56!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-10.jpg" alt="(!LANG:>l IP addresses are allocated globally by a private non-profit corporation called ICANN"> l Распределением IP адресов в мире занимается частная некоммерческая корпорация под названием ICANN (Internet Corporation for Assigned Names and Numbers), а точнее, работающая под ее патронажем организация IANA (Internet Assigned Numbers Authority).!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-11.jpg" alt="(!LANG:>Classic and classless IP addressing">!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-12.jpg" alt="(!LANG:>Development l Initially, the entire space of possible IP addresses was divided into five classes"> Развитие l Первоначальная все пространство возможных IP адресов было разбито на пять классов l принадлежность IP адреса к определенному классу определялась по нескольким битам первого октета l для адресации сетей и узлов использовались только классы А, В и С. l для этих сетей были определены фиксированные маски подсети по умолчанию, равные, соответственно, 255. 0. 0. 0, 255. 0. 0 и 255. 0, которые не только жестко определяли диапазон возможных IP адресов узлов в таких сетях, но и механизм маршрутизации.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-13.jpg" alt="(!LANG:>Address classes in original IP addressing scheme Class First Possible number of bits in"> Классы адресов в первоначальной схеме IP-адресации Класс Первые Возможное число биты в значения сетей узлов в сети октете первого октета А 0 1 -126 16777214 В 10 128 -191 16384 65534 С 110 192 -223 2097152 254 D 1110 224 -239 Используется для многоадресной рассылки (multicast) Е 1111 240 -254 Зарезервирован как экспериментальный!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-14.jpg" alt="(!LANG:>Problems l To obtain the required range of IP addresses, organizations were asked to fill out a registration form ,"> Проблемы l Для получения нужного диапазона IP адресов организациям предлагалось заполнить регистрационную форму, в которой следовало указать текущее число компьютеров и планируемый рост компью терного парка в течение двух лет. l с развитием Интернета такой подход к распределению IP адресов стал вызывать проблемы, особенно острые для сетей класса В. l организациям, в которых число компьютеров не превышало нескольких сотен (скажем, 500), приходилось регистрировать для себя целую сеть класса В. l Поэтому количество доступных сетей класса В стало на глазах «таять» , но при этом громадные диапазоны IP адресов (в нашем примере - более 65000) пропадали зря.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-15.jpg" alt="(!LANG:>Problem Solving l To solve the problem, a classless IP addressing scheme was developed">!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-16.jpg" alt="(!LANG:>Classless Inter. Domain Routing,) , CIDR l missing IP address binding"> Бесклассовая схема IP-адресации (Classless Inter. Domain Routing,), CIDR l отсутствует привязка IP адреса к классу сети и маске подсети по умолчанию l допускается применение так называемых масок подсети с переменной длиной (Variable Length Subnet Mask, VLSM). l Например, если при выделении сети для вышеуказанной организации с 500 компьютерами вместо фиксированной маски 255. 0. 0 использовать маску 255. 254. 0 то получившегося диапазона из 512 возможных IP адресов будет вполне достаточно. Оставшиеся 65 тысяч адресов можно зарезервировать на будущее или раздать другим желающим подключиться к Интернету. Этот подход позволил гораздо более эффективно выделять организациям нужные им диапазоны IP адресов, и проблема с нехваткой IP сетей и адресов стала менее острой.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-17.jpg" alt="(!LANG:>l Calculate the maximum possible number of nodes in any IP network how many bits"> l Рассчет максимально возможного количества узлов в любой IP сети сколько битов содержится в идентификаторе узла, или, иначе, сколько нулей имеется в маске подсети. l Это число используется в качестве показателя степени двойки, а затем из результата вычитается два зарезервированных адреса (сети и широковещания). l Аналогичным способом легко вычислить и возможное количество сетей классов А, В или С, если учесть, что первые биты в октете уже зарезервированы, а в классе А нельзя использовать IP адреса 0. 0 и 127. 0. 0. 0 для адресации сети.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-18.jpg" alt="(!LANG:>LANG IP addresses l All addresses used on the Internet, must register in"> IP-адреса для локальных сетей l Все используемые в Интернете адреса, должны регистрироваться в IANA, что гарантирует их уникальность в масштабе всей планеты. Такие адреса называют реальными, или публичными (public) IP адресами. l Для локальных сетей, не подключенных к Интернету, регистрация IP адресов, естественно, не требуется, так что, в принципе, здесь можно использовать любые возможные адреса. Однако, чтобы не допускать возможных конфликтов при последующем подключении такой сети к Интернету, RFC 1918 рекомендует применять в локальных сетях только следующие диапазоны так называемых частных (private) IP адресов (в Интернете эти адреса не существуют и использовать их там нет возможности): ¡ 10. 0- 10. 255; ¡ 172. 16. 0. 0- 172. 31. 255; а!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-19.jpg" alt="(!LANG:>IP Routing Basics l to properly communicate with other computers and networks , each"> Основы IР-маршрутизации l чтобы правильно взаимодействовать с другими компьютерами и сетями, каждый компьютер определяет, какие IP адреса принадлежат его локальной сети, а какие - удаленным сетям. l если выясняется, что IP адрес компьютера назначения принадлежит локальной сети, пакет посылается непосредственно компьютеру назначения, если же это адрес удаленной сети, то пакет посылается по адресу основного шлюза.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-20.jpg" alt="(!LANG:>Example COMPUTER l IP address - 192. 168. 5. 200 ; l subnet mask -"> Пример КОМПЬЮТЕР l IP адрес - 192. 168. 5. 200; l маска подсети - 255. 0; l основной шлюз - 192. 168. 5. 1. При запуске протокола IP на компьютере выполняется операция логического «И» между его собственными IP адресом и маской подсети l IP адрес в 32 разрядном виде 11000000 10101000 00000101 11001000; l маска подсети - 11111111 0000; l идентификатор сети - 11000000 10101000 00000101 0000 Т. е. 192. 168. 5. 0 идентификатор собственной сети!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-21.jpg" alt="(!LANG:>Example Task: send an IP packet to address 192. 168. 5. 15. l the computer is performing"> Пример Задача: отправить IP-пакет по адресу 192. 168. 5. 15. l компьютер выполняет операцию логического «И» с IP адресом компьютера назначения и собственной маской подсети. l полученный в результате идентификатор сети назначения будет совпадать с идентификатором собственной сети компьютера отправителя.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-22.jpg" alt="(!LANG:>Example him"> Пример Так наш компьютер определит, что компьютер назначения находится в одной с ним сети, и выполнит следующие операции: l с помощью протокола ARP будет определен физический МАС адрес, соответствующий IP адресу компьютера назначения; l с помощью протоколов канального и физического уровня по этому МАС адресу будет послана нужная информация.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-23.jpg" alt="(!LANG:>Example 2 Task: send an IP packet to address 192. 168 10. 20. l The computer will"> Пример 2 Задача: отправить IP-пакет по адресу 192. 168. 10. 20. l Компьютер выполнит аналогичную процедуру определения идентификатора сети назначения. l В результате будет получен адрес 192. 168. 10. 0, не совпадающий с идентификатором сети компьютера отправителя. l Так будет установлено, что компьютер назначения находится в удаленной сети, и алгоритм действий компьютера отправителя изменится: 1. будет определен МАС адрес не компьютера назначения, а маршрутизатора; 2. с помощью протоколов канального и физического уровня по этому МАС адресу на маршрутизатор будет послана нужная информация. Дальнейшая судьба IP пакета зависит от правильной настройки маршрутизаторов, объединя ющих сети 192. 168. 5. 0 и 192. 168. 10. 0. важна !} correct setting subnet masks in IP addressing parameters!!!

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-24.jpg" alt="(!LANG:> Ways to configure IP settings and check if it works 1. manually assign (easy make a mistake when"> Способами настройки параметров IP и проверка работоспособности 1. назначить вручную (легко ошибиться, при изменении надо перенастраивать, сетевые администраторы полностью контролируют все IP адреса, невозможно работать в крупных корпоративных сетях с !} mobile devices such as laptops or PDAs that often move from one network segment to another) 2. automatically obtain an IP address. Dedicated servers that support the Dynamic Host Configuration Protocol (DHCP) f function to serve requests from clients for an IP address and other information necessary for proper network operation. If the DHCP server is not available (missing or not working), then starting from Windows versions 98 computers assign themselves an IP address. This uses the Automatic Private IP Addressing (APIPA) mechanism, for which the address range 169.254.0.0 - 169.254.255 has been registered by Microsoft with IANA.

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-25.jpg" alt="(!LANG:>Checking IP 1. IPCONFIG /ALL. 2 parameters and functionality PING 127."> Проверка параметров и работоспособности протокола IP 1. IPCONFIG /ALL. 2. PING 127. 0. 0. 1 3. PING w. x. y. z, где w. x. y. z - IP адрес соседнего компьютера. 4. PING w. x. y. z, где w. x. y. z - IP адрес основного шлюза. 5. PING w. x. y. z, гдеw. x. y. z - IP адрес любого удаленного компьютера.!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-26.jpg" alt="(!LANG:>Questions 1. What parameters and settings are required to ensure the operation of the TCP protocol stack /IP?2."> Вопросы 1. Какие параметры и настройки обязательны дляобеспечения работы стека протоколов TCP/IP? 2. Что такое IP адрес? Какова его структура? Какиевозможны способы представления IP адресов? 3. Чем отличаются версии 4 и 6 протокола IP? Какие преимущества обеспечит версия 6 протокола IP? Почему возникла необходимость в переходе на версию 6 протокола IP? 4. Что такое маска подсети? Для чего она нужна? 5. В чем заключается смысл разделения IP адреса на идентификаторы сети и узла? Для чего это требуется? 6. Какие IP адреса и маски являются допустимыми, а какие - нет? Почему? 7. В чем различие между классовой и бесклассовой IP адресациями? Каковы их преимущества и недостатки?!}

Src="https://present5.com/presentation/3/159928527_437552731.pdf-img/159928527_437552731.pdf-27.jpg" alt="(!LANG:>Questions 1. What are IP address classes? determined? 2."> Вопросы 1. Что такое классы IP адресов? По каким правилам они определяются? 2. Как назначить IP адреса в локальной сети (без выхода в Интернет)? 3. Каковы основные принципы маршрутизации пакетов в локальных и удаленных сетях? 4. Что такое таблица маршрутов (таблица маршрутизации)? Объясните смысл каждой из ее колонок. 5. Как «прописать» в таблице маршрутизации отсутствующий в ней новый маршрут? 6. Что такое динамическая конфигурация узлов? Для чего она нужна? 7. В чем заключается технология автоматической личной IP адресации? 8. Каков типовой алгоритм проверки работоспособности протокола IP?!}

Internal routing protocol RIP

This routing protocol is designed for relatively small and relatively homogeneous networks. A route is characterized by a distance vector to the destination. It is assumed that each router is the starting point of several routes to the networks with which it is connected. Descriptions of these routes are stored in a special table called route. The RIP routing table contains an entry for each serviced machine (for each route). The entry must include:

Destination IP address.
Route metric (from 1 to 15; number of steps to the destination).
IP address of the nearest router (gateway) on the way to the destination.
Route timers.

Periodically (once every 30 seconds), each router broadcasts a copy of its routing table to all neighboring routers with which it is directly connected. The destination router looks up the table. If there is a new path in the table, or a message about a shorter route, or changes in path lengths have occurred, these changes are recorded by the receiver in its routing table. The RIP protocol must be able to handle three types of errors:

Cyclic routes.

To suppress instabilities, RIP should use a small value of the maximum possible number of steps (no more than 16).

The slow distribution of routing information across the network creates problems when the routing situation changes dynamically (the system does not keep up with the changes). A small limit value of the metric improves convergence, but does not eliminate the problem.

OSPF link state protocol

The OSPF (Open Shortest Path Firs) protocol is an implementation of the link state algorithm (it was adopted in 1991) and has many features oriented to use in large heterogeneous networks.

The OSPF protocol computes routes on IP networks while maintaining other routing information exchange protocols.

Directly connected routers are called neighbors. Each router keeps information about what state it thinks its neighbor is in. A router relies on neighboring routers and only passes data packets to them if it is sure they are fully functional. To find out the status of links, neighbor routers quite often exchange short HELLO messages.

To propagate the state of the links across the network, routers exchange messages of a different type. These messages are called router links advertisement - an advertisement about the router's links (more precisely, about the state of the links). OSPF routers exchange not only their own, but also other people's link announcements, eventually receiving information about the state of all network links. This information forms the network connection graph, which, of course, is the same for all network routers.

BGP protocol

The general scheme of how BGP works is as follows. BGP routers of neighboring ASs that decide to exchange routing information establish BGP connections between themselves and become BGP neighbors (BGP peers).

Next, BGP uses an approach called path vector, which is an evolution of the distance vector approach. BGP neighbors send (announce, advertise) each other path vectors. The path vector, unlike the distance vector, contains not just the network address and distance to it, but the network address and a list of path attributes that describe various characteristics of the route from the source router to the specified network. In what follows, for brevity, we will call the data set consisting of the network address and path attributes to this network a route to this network.

BGP Implementation

A pair of BGP neighbors establishes a TCP connection between themselves, port 179. Neighbors belonging to different ASs must be directly accessible to each other; for neighbors from the same AS, there is no such restriction, since the internal routing protocol will ensure the availability of all necessary routes between nodes of the same autonomous system.

The information flow exchanged between BGP neighbors via TCP consists of a sequence of BGP messages. The maximum message length is 4096 octets, the minimum is 19. There are 4 types of messages.

Protocol RIP (Routing Information Protocol) is one of the oldest protocols for the exchange of routing information, but it is still extremely common in computer networks. In addition to a RIP version for TCP/IP networks, there is also a RIP version for IPX/SPX networks from Novell.

In this protocol, all networks have numbers (the way the number is formed depends on the network layer protocol used in the network), and all routers have identifiers. The RIP protocol makes extensive use of the concept of "distance vector". The distance vector is a set of pairs of numbers that are numbers of networks and distances to them in hops.

Distance vectors are iteratively propagated by routers over the network, and after a few steps, each router has data about the networks it can reach and about the distances to them. If the connection with any network is broken, then the router notes this fact by assigning the maximum possible value to the vector element corresponding to the distance to this network, which has a special meaning - "no connection". This value in the RIP protocol is the number 16.

Figure 8.1 shows an example of a network consisting of six routers with IDs 1 to 6 and six networks A to F formed by direct point-to-point links.

Rice. 8.1. Exchange of routing information using the RIP protocol

The figure shows the initial information contained in the topological base of router 2, as well as information in the same base after two iterations of the exchange of routing packets of the RIP protocol. After a certain number of iterations, router 2 will know the distances to all networks on the Internet, and it may have several alternative options for sending a packet to the destination network. Let in our example, the destination network is network D.

When it needs to send a packet to network D, the router looks up its route database and selects the port that has the shortest distance to the destination network (in this case, the port that connects it to router 3).

A timer is associated with each routing table entry to adapt to changes in the state of links and equipment. If no new message is received within the timeout confirming this route, then it is removed from the routing table.

When using the RIP protocol, the heuristic Bellman-Ford dynamic programming algorithm works, and the solution found with its help is not optimal, but close to optimal. The advantage of the RIP protocol is its computational simplicity, and the disadvantages are the increase in traffic when periodically sending broadcast packets and the non-optimality of the found route.

Figure 8.2 shows a case of unstable network operation via the RIP protocol when the configuration is changed - the communication link between router M1 and network 1 fails. When this connection is operational, each router has an entry in the route table about network number 1 and the corresponding distance to it.

Rice. 8.2. An example of unstable network operation when using the RIP protocol

When the connection with network 1 is broken, router M1 notes that the distance to this network has taken the value 16. However, after receiving a routing message from router M2 after some time that the distance from it to network 1 is 2 hops, router M1 increases this distance by 1 and notes that network 1 is reachable through router 2. As a result, a packet destined for network 1 will circulate between routers M1 and M2 until the network 1 entry in router 2 expires and it transmits this information router M1.

To avoid such situations, routing information about the network known to the router is not transmitted to the router from which it came.

There are other, more complex cases of unstable behavior of networks using the RIP protocol when the state of the links or routers of the network changes.

The global computer network Internet was originally built according to the following scheme: a backbone network, networks called autonomous systems join it. The backbone network is also an autonomous system. This approach is convenient because detailed topological information remains within the autonomous system, and the autonomous system itself as a whole for the rest of the Internet is represented by external gateways (routers through which autonomous systems join the backbone network). Internal gateways are used to form subnets within an autonomous system.

Accordingly, the routing protocols used on the Internet are divided into external and internal. External routing protocols (EGP, BGP) carry routing information between autonomous systems. Internal routing protocols (RIP, OSPF, IS-IS) are used only within the autonomous system. Changing routing protocols and routes within an autonomous system does not affect other autonomous systems.

OSPF (Open Shortest Path First) was adopted in 1991. This is a modern protocol designed to work in large heterogeneous networks with a complex topology, including loops. It is based on the link state algorithm, which is highly resistant to network topology changes.

40.Transport protocols of the TCP/IP stack.

Since connections are not established at the network layer, there is no guarantee that all packets will arrive at their destination unharmed or arrive in the same order in which they were sent. This task - ensuring reliable information communication between two end nodes - is solved by the main layer of the TCP / IP stack, also called the transport layer.

The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) operate at this layer. The TCP protocol provides reliable message passing between remote application processes through the formation of logical connections. This protocol allows peer entities on the sending and receiving computers to communicate in duplex mode. TCP allows error-free delivery of a byte stream generated on one of the computers to any other computer that is part of the composite network. TCP divides the stream of bytes into parts - segments, and transfers them to the underlying level of internetworking. Once these segments have been delivered by the internetworking layer to their destination, TCP will reassemble them into a continuous stream of bytes.

The UDP protocol provides the transfer of application packets in a datagram manner, like the main protocol of the IP internetworking layer, and performs only the functions of a link (multiplexer) between network protocol and numerous application layer services or user processes.

41.TCP/IP diagnostic utilities.

TCP/IP includes diagnostic utilities to check stack configuration and test network connectivity.

Utility	Application
arp	Displays for viewing and editing the address translation table used by the ARP (Address Resolution Protocol) address resolution protocol - determines the local address from an IP address
hostname	Displays the name of the local host. Used without parameters.
ipconfig	Displays values for the current TCP/IP stack configuration: IP address, subnet mask, default gateway address, WINS (Windows Internet Naming Service) and DNS (Domain Name System) addresses
nbtstat	Displays statistics and current information on NetBIOS installed over TCP/IP. Used to check the status of current NetBIOS connections.
netstat	Displays statistics and current information on a TCP/IP connection.
nslookup	Performs verification of records and domain aliases of hosts, domain services of hosts, and information operating system, by querying DNS servers.
ping	Performs validation of TCP/IP configuration and pings to a remote host.
route	Modifies IP routing tables. Displays the contents of the table, adds and removes IP routes.
tracert	Checks the route to remote computer by sending ICMP (Internet Control Message Protocol) echo packets. Displays the path of packets to the remote computer.

The ipconfig utility is used to verify that TCP/IP is configured correctly. This command is useful on computers running Dynamic Host Configuration Protocol (DHCP) as it allows users to determine what TCP/IP network configuration and values have been set using DHCP.
The ipconfig utility allows you to find out if the configuration is initialized and if there are duplicate IP addresses:
- if the configuration is initialized, then the IP address, mask, gateway appears;
- if IP addresses are duplicated, then the netmask will be 0.0.0.0;
- if using DHCP the computer could not obtain an IP address, then it will be equal to 0.0.0.0 .
The ping (Packet Internet Grouper) utility is used to check TCP/IP configuration and diagnose connection errors. It determines the availability and functioning of a particular host. Using ping The best way check that between local computer and the network host has a route.
The ping command verifies a connection to a remote host by sending ICMP echo packets to that host and listening for echo responses. Ping waits for each packet sent and prints the number of packets sent and received. Each received packet is checked against the transmitted message. If communication between hosts is bad, the ping messages will show how many packets are lost.
By default, 4 echo packets are sent, 32 bytes long (a periodic sequence of uppercase alphabetic characters). Ping allows you to change the size and number of packets, specify whether the route it uses should be recorded, what time-to-live (ttl) value to set, whether the packet can be fragmented, etc. When receiving a response, the time field indicates how long ( in milliseconds) the sent packet reaches the remote host and returns back. Because the default value for waiting for a response is 1 second, all values in this field will be less than 1000 milliseconds. If you get a "Request time out" message, it's possible that if you increase the response timeout, the packet will reach the remote host.
Ping can be used to test both the hostname (DNS or NetBIOS) and its IP address. If the ping succeeds with the IP address but fails with the name, the problem is with the address/name match, not with the network connection.
The ping utility is used in the following ways:
1) To verify that TCP/IP is installed and properly configured on the local computer, the loopback address is specified in the ping command feedback(loopback address): ping 127.0.0.1
2) To make sure that the computer is correctly added to the network and the IP address is not duplicated, the IP address of the local computer is used:
ping localhost_ip_address
3) To verify that the default gateway is functioning and that any local host on the local network can be connected, the IP address of the default gateway is set:
ping gateway_ip address
4) To check the possibility of establishing a connection through the router, the ping command specifies the IP address of the remote host:
ping [options] IP address of remote host
Tracert is a route tracing utility. It uses the TTL (time-to-live) field of the IP packet and the ICMP error message to determine the route from one host to another.
The tracert utility can be more informative and convenient than ping, especially in cases where the remote host is unreachable. It can be used to determine the area of communication problems (at the ISP, on the core network, on the remote host network) by how far the route will be tracked. If there are problems, the utility displays asterisks (*) or messages like "Destination net unreachable", "Destination host unreachable", "Request time out", "Time Exeeded".
The tracert utility works like this: it sends 3 probe echo packets to each host through which the route to the remote host passes. At the same time, the response time for each packet is displayed on the screen (It can be changed using a special parameter). Packets are sent with different time-to-live values. Each router along the path decrements the TTL value by one before forwarding the packet. Thus, the lifetime is a counter of intermediate delivery points (hops). When the packet lifetime reaches zero, the router is expected to send an ICMP "Time Exeeded" message to the source computer. The route is determined by sending the first echo packet with TTL=1. The TTL is then incremented by 1 on each subsequent packet until either the packet reaches the remote host or the maximum possible TTL is reached (default 30, set with the -h option). The route is determined by examining the ICMP messages that are sent back by intermediate routers.
Syntax: tracert [options] target_host_name
The ARP utility is designed to work with the ARP cache. The main task of the ARP protocol is to translate IP addresses to the corresponding local addresses. To do this, the ARP protocol uses information from the ARP table (ARP cache). If the required entry in the table is not found, then the ARP protocol sends a broadcast request to all computers on the local subnet, trying to find the owner of this IP address. The cache can contain two types of entries: static and dynamic. Static entries are entered manually and stored in the cache permanently. Dynamic entries are cached as a result of broadcast requests. For them there is a concept of lifetime. If within a certain time (by default 2 minutes) the entry has not been claimed, then it is removed from the cache.
The netstat utility allows you to get static information on some of the stack protocols (TCP, UDP, IP, ICMP), and also displays information about current network connections. It is especially useful on firewalls, and can be used to detect network perimeter security breaches.
Syntax:
netstat [-a] [-e] [-n] [-s] [-p protocol] [-r]
Options:
-a lists all network connections and listening ports on the local computer;
-e displays statistics for Ethernet interfaces (for example, the number of bytes received and sent);
-n displays information on all current connections (for example, TCP) for all network interfaces of the local computer. For each connection, information about the IP addresses of the local and remote interfaces is displayed along with the numbers of the ports used;
-s displays statistical information for UDP, TCP, ICMP, IP protocols. The "/more" key allows you to view information page by page;
-r displays the contents of the routing table.

TCP/IP communication protocol

The Internet, which is a network of networks and unites a huge number of different local, regional and corporate networks, functions and develops thanks to the use of a single TCP / IP data transfer protocol. The term TCP/IP includes the names of two protocols:

Transmission Control Protocol (TCP) - transport protocol;
Internet Protocol (IP) is a routing protocol.

Routing protocol. The IP protocol provides for the transfer of information between computers on a network. Let's consider the operation of this protocol by analogy with the transfer of information using regular mail. In order for the letter to reach its destination, the address of the recipient (to whom the letter is) and the address of the sender (from whom the letter is from) are indicated on the envelope.

Similarly, information transmitted over the network is "packed into an envelope" on which the IP addresses of the recipient's and sender's computers are "written", for example, "To: 198.78.213.185", "From: 193.124.5.33". The contents of the envelope in computer language is called by IP packet and is a set of bytes.

In the process of forwarding ordinary letters, they are first delivered to the post office closest to the sender, and then transferred along the chain of post offices to the post office closest to the recipient. At intermediate post offices, letters are sorted, that is, it is determined to which next post office a particular letter must be sent.

IP packets on the way to the recipient computer also pass through numerous intermediate Internet servers on which the operation is performed. routing. As a result of routing, IP packets are sent from one Internet server to another, gradually approaching the recipient computer.

Internet Protocol (IP) provides routing of IP packets, that is, the delivery of information from the sending computer to the receiving computer.

Determination of the route of information passage. The "geography" of the Internet differs significantly from the geography we are accustomed to. The speed of obtaining information does not depend on the remoteness of the Web server, but on the number of intermediate servers and the quality of the communication lines (their bandwidth) through which information is transmitted from node to node.

You can get acquainted with the route of information on the Internet quite simply. Special Program tracert.exe, which is included with Windows, allows you to track through which servers and with what delay information is transmitted from the selected Internet server to your computer.

Let's see how access to information is realized in the "Moscow" part of the Internet to one of the most popular search servers of the Russian Internet www.rambler.ru.

Determination of the information flow path

2. In the window MS-DOS session in response to the system prompt to enter the command .

3. After a while, a trace of information transfer will appear, that is, a list of nodes through which information is transmitted to your computer, and the time of transmission between nodes.

The tracing of the information transfer route shows that the www.rambler.ru server is at a "distance" of 7 hops from us, i.e. the information is transmitted through six intermediate Internet servers (through the servers of Moscow providers MTU-Inform and Demos). The speed of information transfer between nodes is quite high, one "transition" takes from 126 to 138 ms.

transport protocol. Now imagine that we need to send a multi-page manuscript by mail, but the post office does not accept parcels and parcels. The idea is simple: if the manuscript does not fit into a regular postal envelope, it should be sorted into sheets and sent in several envelopes. At the same time, the sheets of the manuscript must be numbered, so that the recipient knows in what sequence these sheets should be joined later.

On the Internet, a similar situation often occurs when computers exchange large files. If you send such a file in its entirety, then it can "clog" the communication channel for a long time, making it inaccessible for sending other messages.

To prevent this from happening, on the sender computer, it is necessary to split a large file into small parts, number them and transport them in separate IP packets to the recipient computer. On the receiving computer, you need to assemble the source file from the individual parts in the correct sequence.

Transmission Control Protocol (TCP), that is, the transport protocol, provides for splitting files into IP packets during transmission and assembling files during receipt.

Interestingly, for the IP protocol responsible for routing, these packets are completely unrelated to each other. Therefore, the last IP packet may well overtake the first IP packet along the way. It may happen that even the delivery routes of these packages will be completely different. However, TCP will wait for the first IP packet and reassemble the source file in the correct sequence.

Determination of the time of exchange of IP packets. The time of IP packet exchange between the local computer and the Internet server can be determined using the ping utility, which is part of the operating system. Windows systems. The utility sends four IP packets to the specified address and shows the total transmission and reception time for each packet.

Determination of IP packet exchange time

1. Connect to the Internet, enter the [Programs-MS-DOS Session] command.

2. In the window MS-DOS session in response to the system prompt to enter the command .

3. In the window MS-DOS session the result of the test passage of the signal in four attempts will be displayed. The response time characterizes the speed parameters of the entire chain of communication lines from the server to the local computer.

Questions for reflection

1. What ensures the holistic functioning of the global computer network Internet?

Practical tasks

4.5. Track the route of information from one of the most popular Internet search servers www.yahoo.com, located in the "American" segment of the Internet.

4.6. Determine the time of exchange of IP packets with the www.yahoo.com server.