HCIA notes

HCIA-OSI

OSI: Open system interconnection communication reference model （ English ：Open System Interconnection Reference Model, Abbreviation for OSI）, Referred to as OSI Model （OSI model）, A conceptual model , Proposed by the international organization for standardization , A standard framework that attempts to interconnect computers worldwide as networks .
This model divides the work of network communication into 7 layer , Namely The physical layer , Data link layer , The network layer , Transport layer , The session layer , Presentation layer and application layer .1 to 4 Layers are considered lower layers , These layers are closely related to data movement .5 to 7 The first floor is the top floor , Contains application level data . Each layer is responsible for a specific work , Then transfer the data to the next layer .
application layer , The session layer , The presentation layer ------------------ Control level
Transport layer , The network layer , Data link layer , The physical layer ----- Data level

The seventh floor ： application layer

Receive user data , Interface of human-computer interaction , For applications , Is dedicated to applications .

The sixth floor ： The presentation layer

Logic language （ Software language ） Convert to machine language （ Binary language ）, translate , encryption .

The fifth floor ： The session layer

At the conversation level and above , The unit of data transmission is no longer named , Collectively referred to as message . For each type of data transmitted （ management ： establish 、 maintain 、 End ） A virtual link （ In order to prevent different types of data from affecting each other ）.

The fourth level ： Transport layer

The first 4 The data unit of layer is also called packet （packets）.TCP The unit of data is called segment （segments） and UDP The data unit of the protocol is called “ The datagram （datagrams）”. The first 4 Layer provides end-to-end communication management . image TCP And other protocols are very good at ensuring the reliability of communication . Some protocols don't care if some packets are lost ,UDP The agreement is a major example . effect ：1. Distinguish traffic 2. Define the data transmission mode .
TCP： Transmission control protocol , Is a reliable connection oriented transport protocol
UDP： User datagram protocol , It is a non connection oriented and unreliable protocol
TCP data structure
UDP data structure

Three times mobile phone system ： Ensure connection oriented , Also known as TCP Three handshakes of .
Acknowledgement mechanism ： Explicit confirmation Implicit confirmation
Segmented transmission of data ： Transmit larger data according to MTU Value for segmented transmission .
MTU： Maximum transmission unit , Default 1500 byte .
4 layer PDU：segment piecewise Fragmentation

The third level ： The network layer

The task of the network layer is to select the appropriate inter network routing and switching nodes , Make sure the data is transmitted in time . The network layer consists of the frames provided by the data link layer , The network layer packet header is encapsulated in the packet , It contains logical address information - - Network address of source site and destination site address . Addressing , Addressing .
Addressing protocol ：IP（IPV4 \ IPV6）
IP Address ：32 It's binary ,0 and 1 Constitute for addressing
Network mask ：32 It's binary , Successive 1+ Successive 0 constitute , Successive 1 Represents the network bit , Successive 0 Represents the host bit .
Address classification ：
A Class address ： The first is fixed as 0
0XXX XXXX --0-127(1-126), The netmask defaults to 255.0.0.0
B Class address ： The first two are fixed as 10
10XX XXXX --128-191, The netmask defaults to 255.255.0.0
C Class address ： The first three are fixed as 110
110X XXXX–192-223, The netmask defaults to 255.255.255.0
D Class address ： The first four are fixed as 1110
1110 XXXX–224-239, Multicast address , No mask
E Class address ： The first four are fixed as 1111
1111 XXXX --240-255, Scientific research address

Special address

1.0.X.X.X Invalid address （ Reserved address ）,0.0.0.0 Invalid address placeholder
2.127.0.0.1 Local testing （127.X.X.X Address of the test ）
3. network number , The network bit remains unchanged All hosts are 0 The address of （ Describe a network segment ）
162.1.1.1------------------162.1.0.0 255.255.0.0
255.255.0.0
4. Restricted broadcast address ,255.255.255.255
5. directional （ direct ） Broadcast address , The network bit remains unchanged , All hosts are 1
200.1.1.1 —> 200.1.1.255
255.255.255.0
6. Local link address ：link-local { 169.254.0.0 255.255.0.0 }
A B C Class addresses are called unicast addresses
unicast ： One to one transmission
Multicast ： One to many transmission
radio broadcast ： One to all transmission modes
Three layers PDU：packet package

The second floor ： Data link layer

LAN （ Ethernet Ethernet） Wide area network （PPP HDLC ATM FR ）
Second floor address ：Mac Address （ Media access control ）— Physical address Hardware address Burn address
LLC layer ： Logical link control sublayer
MAC layer ： Media access control sublayer

Mac Address structure ： 48 It's binary , Writing uses 12 Hexadecimal （ A hexadecimal needs to use 4 individual Binary representation ） The way of writing ： Subtractive hexadecimal or dotted hexadecimal .
front 24 position ： manufacturer ID ----OUI（ Uniform resource identifiers ）
after 24 position ： product ID ----interface ID （ Interface identifier ）
On the second floor PDU ：frame frame

first floor ： The physical layer

Focus on Mechanical characteristics of network hardware Optical properties Electrical characteristics
First floor PDU：bit Bit stream
Transmission medium ：
Wired media ： Optical fiber 、 Twisted pair （RJ45） Coaxial cable
Wireless media ：WiFi , bluetooth
Twisted pair ： RJ45 Line
568A Linear sequence ： Green and white 、 green 、 Orange white 、 blue 、 Bluish white 、 orange 、 Brown and white 、 Brown
568B Linear sequence ： Orange white 、 orange 、 Green and white 、 blue 、 Bluish white 、 green 、 Brown and white 、 Brown
Parallel lines ： Also known as the through line , Same line sequence . Parallel lines are used for different layers of equipment .
Cross line ： The line sequence is different . Cross lines are used for equipment on the same floor .
All negative ： Also known as console Line , Configuration line , The line sequence is opposite , Network equipment for user control .

Router ： Third floor equipment , distinguish IP Address . Different interfaces are in different network segments （ Broadcast area ）
Switch （ bridge ）： Second floor equipment , Use MAC Address , All interfaces are in the same broadcast domain by default , One Interface is a conflict domain .
A hub （hub）： amplifier Amplify the signal , Belong to 1 Floor equipment , distinguish bit flow ,hub All interfaces on the Are in the same conflict domain .
host （ The server ）

TCP/IP Model

application layer （ application layer The presentation layer The session layer ）
Host to host layer （ Transport layer ）
The Internet layer （ The network layer ）
Network interface layer （ Data link layer The physical layer ）

Data encapsulation ： The process of generating data
Data unpacking ： The process of receiving data for reading