середа, 23 листопада 2016 р.
четвер, 17 листопада 2016 р.
Static
If you make the member Static, it will be shared by all the objects which you will create. There will always be only 1 copy of the Static member in the memory, no matter how many objects you will create.
середа, 16 листопада 2016 р.
ARP
ARP (англ. Address Resolution Protocol — протокол определения адреса) — протокол в компьютерных сетях, предназначенный для определения MAC-адреса по известному IP-адресу.
Рассмотрим суть функционирования ARP на простом примере. Компьютер А (IP-адрес 10.0.0.1) и компьютер Б (IP-адрес 10.22.22.2) соединены сетью Ethernet. Компьютер А желает переслать пакет данных на компьютер Б, IP-адрес компьютера Б ему известен. Однако сеть Ethernet, которой они соединены, не работает с IP-адресами. Поэтому компьютеру А для осуществления передачи через Ethernet требуется узнать адрес компьютера Б в сети Ethernet (MAC-адрес в терминах Ethernet). Для этой задачи и используется протокол ARP. По этому протоколу компьютер А отправляет широковещательный запрос, адресованный всем компьютерам в одном с ним широковещательном домене. Суть запроса: «компьютер с IP-адресом 10.22.22.2, сообщите свой MAC-адрес компьютеру с МАС-адресом (напр. a0:ea:d1:11:f1:01)». Сеть Ethernet доставляет этот запрос всем устройствам в том же сегменте Ethernet, в том числе и компьютеру Б. Компьютер Б отвечает компьютеру А на запрос и сообщает свой MAC-адрес (напр. 00:ea:d1:11:f1:11) Теперь, получив MAC-адрес компьютера Б, компьютер А может передавать ему любые данные через сеть Ethernet.
MAC-address
MAC, Media Access Control, address is a globally unique identifier assigned to network devices, and therefore it is often referred to as hardware or physical address. MAC addresses are 6-byte (48-bits) in length, and are written in MM:MM:MM:SS:SS:SS format. The first 3-bytes are ID number of the manufacturer, which is assigned by an Internet standards body. The second 3-bytes are serial number assigned by the manufacturer.
Difference between TCP and UDP
Difference between TCP and UDP
| TCP | UDP |
| Reliability: TCP is connection-oriented protocol. When a file or message send it will get delivered unless connections fails. If connection lost, the server will request the lost part. There is no corruption while transferring a message. | Reliability: UDP is connectionless protocol. When you a send a data or message, you don’t know if it’ll get there, it could get lost on the way. There may be corruption while transferring a message. |
| Ordered: If you send two messages along a connection, one after the other, you know the first message will get there first. You don’t have to worry about data arriving in the wrong order. | Ordered: If you send two messages out, you don’t know what order they’ll arrive in i.e. no ordered |
| Heavyweight: – when the low level parts of the TCP “stream” arrive in the wrong order, resend requests have to be sent, and all the out of sequence parts have to be put back together, so requires a bit of work to piece together. | Lightweight: No ordering of messages, no tracking connections, etc. It’s just fire and forget! This means it’s a lot quicker, and the network card / OS have to do very little work to translate the data back from the packets. |
| Streaming: Data is read as a “stream,” with nothing distinguishing where one packet ends and another begins. There may be multiple packets per read call. | Datagrams: Packets are sent individually and are guaranteed to be whole if they arrive. One packet per one read call. |
| Examples: World Wide Web (Apache TCP port 80), e-mail (SMTP TCP port 25 Postfix MTA), File Transfer Protocol (FTP port 21) and Secure Shell (OpenSSH port 22) etc. | Examples: Domain Name System (DNS UDP port 53), streaming media applications such as IPTV or movies, Voice over IP (VoIP), Trivial File Transfer Protocol (TFTP) and online multiplayer games etc |
HTTP, HTTPS, SSH, SSL and TLS protocols
HTTP - Hypertext Transfer Protocol
application protocol responsible for transfer data. HTTP functions as a request–response protocol in the client–server computing model. A web browser, for example, may be the client and an application running on a computer hosting a website may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, returns a response message to the client. The response contains completion status information about the request and may also contain requested content in its message body.
HTTPS
is a protocol for secure communication over a computer network which is widely used on the Internet. HTTPS consists of communication over Hypertext Transfer Protocol (HTTP) within a connection encrypted by Transport Layer Security or its predecessor, Secure Sockets Layer.
SSL - Secure Sockets Layer
is a standard security technology for establishing an encrypted link between a server and a client—typically a web server (website) and a browser, or a mail server and a mail client (e.g., Outlook).
TSL - Transport Layer Security
the same as SSL but new
SSH - Secure Shell
The best known example application is for remote login to computer systems by users. SSH provides a secure channel over an unsecured network in a client-server architecture, connecting an SSH client application with an SSH server
application protocol responsible for transfer data. HTTP functions as a request–response protocol in the client–server computing model. A web browser, for example, may be the client and an application running on a computer hosting a website may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, returns a response message to the client. The response contains completion status information about the request and may also contain requested content in its message body.
HTTPS
is a protocol for secure communication over a computer network which is widely used on the Internet. HTTPS consists of communication over Hypertext Transfer Protocol (HTTP) within a connection encrypted by Transport Layer Security or its predecessor, Secure Sockets Layer.
SSL - Secure Sockets Layer
is a standard security technology for establishing an encrypted link between a server and a client—typically a web server (website) and a browser, or a mail server and a mail client (e.g., Outlook).
TSL - Transport Layer Security
the same as SSL but new
SSH - Secure Shell
The best known example application is for remote login to computer systems by users. SSH provides a secure channel over an unsecured network in a client-server architecture, connecting an SSH client application with an SSH server
How is the lack of IP addresses being solved today?
NAT - Network Address Translation
devices, increasingly popular in homes and offices, allow multiple machines to share a single Internet address.
devices, increasingly popular in homes and offices, allow multiple machines to share a single Internet address.
IP, IPv4, IPv6
IP address
is short for Internet Protocol address. An IP address is an identifier for a computer or device on a TCP/IP network. The format of IP address is a 32-bit numeric address written as four numbers
IPv4
is a 32-bit numeric address written in decimal as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240
IPv6
In IPv6 the IP address size increased from 32-bits to 128-bits. IPv6 adress written in hexadecimal and separated by colons. An example IPv6 address could be written like this: 3ffe:1900:4545:3:200:f8ff:fe21:67cf
is short for Internet Protocol address. An IP address is an identifier for a computer or device on a TCP/IP network. The format of IP address is a 32-bit numeric address written as four numbers
IPv4
is a 32-bit numeric address written in decimal as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240
IPv6
In IPv6 the IP address size increased from 32-bits to 128-bits. IPv6 adress written in hexadecimal and separated by colons. An example IPv6 address could be written like this: 3ffe:1900:4545:3:200:f8ff:fe21:67cf
Differnces between hub, roter and switch
1. Hub
very primitive device. It creates a network between computers. it is impossible to manage it. If one computer send package to the another, this package is sending to the all computers in the network
2. Switch
also create a network. One computer can send package to the another. Only this computer will receive this package
3. Router
connect networks. Links computer to the Internet. Via router you can send data between netorks
very primitive device. It creates a network between computers. it is impossible to manage it. If one computer send package to the another, this package is sending to the all computers in the network
2. Switch
also create a network. One computer can send package to the another. Only this computer will receive this package
3. Router
connect networks. Links computer to the Internet. Via router you can send data between netorks
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