Network Security day01_ Computer network and layered thought

2018.9.1 Network security day01_ computer network and stratification thought Layered thought of network security computer NetworkLAN and WAN LAN (local area network)-Lan

A local areanetwork, or LAN, is a group of computers interconnected by multiple computers within a region. "One area" means the same office, the same building, the same company and the same school, usually within a radius of thousands of meters. LAN can achieve file management, application software sharing, printer sharing, scanner sharing, workgroup scheduling, e-mail and fax communication services and other functions. The local area network is closed, can be composed of two computers in the office, can also be composed of thousands of computers within a company.
-Range: Around 1km
-function: Used to connect computers within a shorter distance
-Typical application: Enterprise network, Campus Network

Wan (Wide area Network)--Wan

Wan, or WAN, is a collection of computer networks spanning large, regional Wide. Usually across provinces, cities, and even a country. A wide area network consists of a large and small subnet, which can be a local area network or a small WAN.
-Range: Dozens of to by M
-Role: For connecting long-distance computer networks
-Typical application: Internet

• LAN and WAN the difference between the LAN is in a certain area, and wan to cross the larger region, then how to define this area? For example, a large company headquartered in Beijing, and branches across the country, if the company will all the branches are connected through the network, then a branch is a LAN, and the entire head office network is a WAN.

Computer network Reference Model

• Layered model
  • Layered thinking
  • OSI Reference Model
  • TCP/IP protocol cluster
• Data transfer process
  • Data encapsulation and solution encapsulation process

Layered model

Because a single huge protocol will increase the difficulty of network design, but also not conducive to the analysis of search problems
The layered model is a design method for developing the network, which describes the communication problem divided into several small problems (layers), each with one level, the same protocol between the same layer

Layered thinking

Define protocol standards with communication requirements

What if you need too many protocols to complete everything?

For example, the process chain behind the behavior of drinking milk, we use layered thinking is listed as follows:

The ranch is milking milk--the Transportation department transports the milk to the factory--and the factory to the milk disinfection--after the supermarket sells--consumers buy milk--drink milk

If this process is not handled separately, the person who drinks the milk must have all the skills of the above process to be able to drink the milk
However, people who enjoy the milk only need to buy and drink, do not care about the previous process is how to complete

Similarly, in the network we complete a data transmission process is extremely complex, and we do not need to understand each, so the use of layered thinking to simplify the process, we only pay attention to drink milk this thing can, do not care about milk production and sales process.

Another example of the process of writing a letter:

A to B in region a write to:

Krabi Area		Area B
Write		Receive Letter
↓		↑
Give the letter to the Post office		Send the letter to the B-hand
↓		↑
The Transport Department sends the letter to the Post office in the receiving area.	→	The Post office received a letter from the Transport Department

The writer does not need to know the specific process of the message transmission, so the person who uses the network does not need to know the data transmission process

Benefits of Tiering:

• reduces the complexity of the process
• each layer is independent, and has an inter-collaborative relationship

OSI Reference Model

In order to reduce the complexity of the network communication process, the 1974 ISO organization proposed the OSI reference Model

OSI (open System interconnect), which is open systems interconnection.
Commonly called the OSI Reference Model, is the network interconnection model that the ISO (International Organization for Standardization) organization studied in the 1985. The architecture standard defines a seven-layer framework for Network interconnection (physical layer, Data link layer, network layer, transport layer, Session layer, presentation layer, and Application layer), the OSI Open System Interconnect Reference Model. In this framework, the functionality of each layer is further elaborated to achieve interoperability, interoperability, and portability of applications in an open system environment.

OSI layer Seven Protocol

The OSI Reference Model divides the network into seven layers

Number of layers	name	function	function
Seventh floor	Application Layer	Provide user interface	file, print, message, database, and application services
Sixth floor	Presentation Layer	Representation of data, encryption, and other processing	Data encryption, compression, and Transformation Services
Fifth Floor	Session Layer	Separating data from different applications	Dialog control
Fourth floor	Transport Layer	Provides reliable or unreliable transmission and performs error correction prior to retransmission	Port-to-port connectivity
Third floor	Network layer	Provide logical addresses that routers use to select paths	Route selection
Second floor	Data Link Layer	Splits a grouping into bytes and combines bytes into frames, provides media access using MAC addresses, performs error detection but does not correct	Framing
First floor	Physical Layer	Transfer bits between devices, specifying levels, cable speeds, and cable pins	Physical topology

The

Learning network needs to be familiar with the relevant protocols and principles of each layer, which will be learned in detail later in the collation.