What is Network and How Does it Work ? (Basics)

If you want to be a good penetration tester, ethical hacker or even black hat hacker you need to know what is Network and how does it work. I decided to start, let's call it "free networking course" consisting of several lessons. So, let's start with first lesson: Basics of networking and terminology.

Network

A computer network or data network is a telecommunications network which allows computers to exchange data. In computer networks, networked computing devices exchange data with each other using a data link. The connections between nodes are established using either cable media or wireless media.

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IP

Short for Internet Protocol address, an IP or IP address is a number (example shown right) used to indicate the location of a computer or other device on a network using TCP/IP. These addresses are similar to those of your house; they allow data to reach the appropriate destination on a network and the Internet. There are two types of addresses used today, IPv4 and IPv6. Although you may only deal with an IPv4 address in your local home, school, or small office you should also be aware of IPv6 addresses for when you encounter them.

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TCP

There are two types of Internet Protocol (IP) traffic. They are TCP or Transmission Control Protocol and UDP or User Datagram Protocol. TCP is connection oriented – once a connection is established, data can be sent bidirectional. TCP is suited for applications that require high reliability, and transmission time is relatively less critical. It is used by HTTP, HTTPS, FTP... We will learn about those in next lesson.

UDP

UDP is a simpler, connectionless Internet protocol. Multiple messages are sent as packets in chunks using UDP. UDP is suitable for applications that need fast, efficient transmission, such as games. UDP's stateless nature is also useful for servers that answer small queries from huge numbers of clients. UDP is used by DNS, DHCP, TFTP...

Switch

Switches are used to connect multiple devices on the same network within a building or campus. For example, a switch can connect your computers, printers and servers, creating a network of shared resources. The switch, one aspect of your networking basics, would serve as a controller, allowing the various devices to share information and talk to each other. Through information sharing and resource allocation, switches save you money and increase productivity. There are two types of switched, managed and unmanaged. Unmanaged works from box, and does not allow you to make changes while managed is more flexible.

Router

Routers, the second valuable component of your networking basics, are used to tie multiple networks together. For example, you would use a router to connect your networked computers to the Internet and thereby share an Internet connection among many users. The router will act as a dispatcher, choosing the best route for your information to travel so that you receive it quickly. Routers analyze the data being sent over a network, change how it is packaged, and send it to another network, or over a different type of network. They connect your business to the outside world, protect your information from security threats, and can even decide which computers get priority over others.

Port

A port number is a way to identify a specific process to which an Internet or other network message is to be forwarded when it arrives at a server. For the Transmission Control Protocol and the User Datagram Protocol, a port number is a 16-bit integer that is put in the header appended to a message unit. This port number is passed logically between client and server transport layers and physically between the transport layer and the Internet Protocol layer and forwarded on.

MAC address

The MAC (Media Access Control) address is your computer's unique hardware number. When you're connected to the Internet from your computer (or host as the Internet protocol thinks of it), a correspondence table relates your IP address to your computer's physical (MAC) address on the LAN.

Subnet mask

A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s.

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