OSI model notes

ISO— International Organization for Standardization
OSI ： Open system interconnection （ Reference model ）
OSI： Open Systems Interconnection model （open organization interconnection）
Suggest OSI Model purpose ： Make communication between different systems easy , It does not require any changes to the logical structure of its low-level hardware and software .
Be careful ：OSI The model is not a protocol , It's a model .（ Focus on Theory ）
TCP/IP Reference model ：TCP/IP It is a layered protocol composed of interacting modules , Each layer provides a specific function , No interdependence .

TCP/IP----TCP/IP Routing technology Volume I Volume two （CCIE）jeff
application layer , The presentation layer , The session layer ----- Control level
Transport layer , The network layer , Data link layer , The physical layer ---- Data level
Layered thinking

application layer （7 layer ）： Receive user data , Interface of human-computer interaction , Application oriented .

The presentation layer （6 layer ）： Logic language （ Software language ） Convert to machine language （ Binary language ）, translate , encryption

The session layer （5 layer ）： For each kind of data transmitted （ Traffic ） establish （ management ： maintain 、 End ） One
Virtual connection （ In order to prevent different types of data from affecting each other, the control level ： The top three
Data level ： The next four floors

Transport layer （4 layer ）： 1. Distinguish traffic 2. Define the data transmission mode
OSI
Port number ： port ID , Range of values 1-65535
Static port ： Also known as indicating port range 1-1023（ Correspond to the flow one by one , Binding relationship ）
Dynamic port ： Range 1024-65535 （ Correspond to the flow one by one , No binding ）
Common port numbers ：
HTTP—80 TCP
HTTPS —443 TCP
RIP----520 UDP
Telnet— Remote login service 23 TCP
SSH ---- Remote login （ High security encryption authentication ）,22 TCP
DNS---- Domain name resolution ,53 TCP and UDP
Unreliable transmission mode and flow characteristics ：1. Large flow 2. High real-time performance 3. Insensitive to data loss
reliable ： How to ensure reliability ？ 1. Acknowledgement mechanism 2. Retransmission mechanism
TCP： Transmission control protocol , Is a reliable connection oriented transport protocol
UDP： User datagram protocol , It is a non connection oriented unreliable transmission protocol

TCP data structure ：

UDP data structure ：

Connection oriented ： Before transmitting data , Both parties negotiate to ensure that the data can be transmitted .
How to ensure connection oriented ？（ Three times mobile phone system ）
Three times mobile phone system ： Ensure connection oriented , Also known as TCP Three handshakes of
Three times handshake between host and server
Synchronization request ：syn req confirm ：Ack
like ： The first handshake . Host synchronization request server port
The second handshake . The server port responds to the confirmation and synchronizes the request host
The third handshake . The host confirms the server port

Acknowledgement mechanism ： Explicit confirmation Implicit confirmation
Optimization mechanism ： Flow control mechanism （ Sliding window mechanism ）; Reorder
Segmented transmission of data ： When transmitting large data, follow MTU Value for segmented transmission .
MTU： Maximum transmission unit , The default is 1500 byte , You can modify （ But not recommended ） expand ：
Bit ---- The bit （ The smallest unit of the Internet ） A binary 【0 1】
1000bit=1kb
1000kb=1Mb
1000Mb=1Gb
1000Gb=1Tb
1000Tb=1Pb
file system (NTFS) of use 210=1024
Byte： byte , A byte is 8 individual bit
1000B=1KB
1000KB=1MB
1000MB=1GB
1000GB=1TB
Rate unit ：
100Mbps=100 mega The bit Per second 12.5MBPS=12.5 mega byte Per second
PDU： Protocol data unit
PDU The representation of data in different layers
4 layer PDU（ Proper noun ）：segment piecewise Fragmentation

The network layer (3 layer )： Addressing Addressing
Address ：
Addressing protocol ： IP （IPV4 IPV6） IPX apple talk novell NSAP
IPv4： use 32 Binary addressing .
A binary be called 1 position bit .
128 64 32 16 8 4 2 1
IP Address （ Generally refer to ipv4）：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 .
Network bit Host bit
1101 1000.0001 0001.0000 0001.0000 0001
216.17.1.1
Simple algorithm ：0000 0001=1
0000 0010=2
0000 0100=4
0000 1000=8
0001 0000=16
0010 0000=32
0100 0000=64
1000 0000=128
255.255.0.0
1111 1111.1111 1111.0000 0000.0000 0000

Write a complete IP Address time ：IP Address + Network mask
Address classification ：
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
A Class address ： The first is fixed as 0
( front 8 Bit is network bit , after 24 Bit host bit )2 To the seventh power of ,2 Of 24 Power IP
0XXX XXXX —0-127（1-126）, The netmask defaults to 255.0.0.0
B Class address ： The first two are fixed as 10
（ front 16 Bit is network bit , after 16 Host location ）2 Of 14 Power network segment ,2 Of 16 Power host bits
10XX XXXX—r, The netmask defaults to 255.255.0.0
C Class address ： The first three are fixed 110
110X XXXX—192-223, The netmask defaults to 255.255.255.0
（ front 24 Bit is network bit , after 8 Bit is host bit ）
（A,B,C Class address is unicast address , Identify only one user ）
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 （ Used to 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 }

Public address ： Globally unique identification address
Private address ： Address without unique identification
10.0.0.0 255.0.0.0
172.{16-31}.0.0 255.255.0.0
192.168.X(0-255).0 255.255.255.0
Three layers PDU：packet package

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

Data link layer （2 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 hex requires
Use 4 A binary representation ） The way of writing ： Subtractive hexadecimal or dotted hexadecimal
60-F2-62-3C-E3-53 Minus hexadecimal ）----- terminal host The server mobile phone
60F2.623C.E353 Point sixteen mechanism ）---- Connect to the device Router A firewall ASA
front 24 position ： manufacturer ID ----OUI（ Uniform resource identifiers ）
after 24 position ： product ID ----interface ID （ Interface identifier ）
On the second floor （ data ）PDU ：frame frame

The physical layer （1 layer ）： Focus on Mechanical characteristics of network hardware Optical properties Electrical characteristics
First floor PDU：bit Bit stream
Transmission medium ： Optical fiber 、 Twisted pair （RJ45）
Ethernet cable ：8 strip ----4 paragraph ---- Twisted in two
Wired media ： Coaxial cable , Twisted pair , Optical fiber
Wireless media ：WiFi, bluetooth ,wimax
Coaxial cable : Thick cable （10mbps transmission distance 500m) Thin cable
Optical fiber ： Single mode fiber （ Single light source , Linear transmission ）
Multimode fiber （ It can transmit many kinds of light ）

Twisted pair ：
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

Divide by line sequence ：
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 .

Shielded twisted pair （STP）;（ Plus metal cover , Shielding interference ）
Unshielded twisted pair （UTP）

weak current
Strong electricity

Classify according to the degree of twist ：3 class 4 class —（10Mbps） 5 class super 5 class —（100Mbps） 6 class super 6 class （1000Mbps– stay 6 Class line 8 Roots are used at the same time ）
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