Shulou(Shulou.com)06/01 Report--

I. Network protocol model

1.OSI Seven-layer Network Protocol Model

OSI layer 7 Protocol (Open System Interconnection): the network connection process is divided into several layers (layer). Each layer has a specific independent function, and the program code of each layer can be written independently, and the functions of each layer will not interfere with each other.

Description:

1) the layer closer to the hardware is the layer1, and the closer to the application is the layer7.

2) either the receiver or the sender, each layer only knows the same level of data of the other party

3) each layer has its own unique header data header to inform the other party of the information, and the subsequent data is real data.

(1) physical layer Physical Layer

Define the voltage and signal of the transmission equipment, connect the data frame to convert into the coding mode of the bit stream, and finally connect the actual transmission medium to send / receive the bit signal.

(2) data Link layer Data-Link Layer

The lower layer is the definition of entity, and the upper layer is the definition of software encapsulation. The data link layer can be divided into two layers:

Biased towards hardware media: MAC data frames, media Access Control frame, the main data packets that can be handled by the network interface, are encoded into bitstreams by the physical layer

Software bias: logical link layer (Logical Link Control) multitasking processes packet data from the upper layer and converts it to MAC format

Information exchange, flow control, data problem processing

(3) Network layer Etwork Layer

Define IP (Internet Protocol) and routing concepts, establish, terminate and maintain connections between computers, and choose the transmission path of data packets.

(4) Transport layer Transport Layer

Connection technologies between sender and receiver, such as TCP, UDP... Including packet format, packet transmission, flow control, frame detection and retransmission during transmission.

(5) session layer Session Layer

Define the connection and disruption of the connection channel between the two limbs, and confirm the establishment of the connection in determining the network service.

You can also establish application sessions and provide other enhanced services

(6) presentation layer Presentation Layer

Data format conversion between network services (or programs): converts or re-encodes data from local applications to the standard format of the network

Encryption and decryption technology

(7) Application layer Appliation Layer

The application does not belong to the application itself and is used to manage the same scheduling data corresponding to the application that it sends and receives.

Define how the application enters the communication interface at this layer to receive or send data to the application and eventually show it to the user

2.TCP/IP protocol

TCP/IP protocol is simplified to a four-layer structure in the concept of OSI seven-layer protocol, and it is not as strict as OSI seven-layer protocol in structure, but it is easy to be widely used in programming.

TCP/IP protocol integrates the application layer, presentation layer and session layer into the application layer.

Application layer: encapsulates data for a specific protocol used in a TCP/IP protocol group and hands it over to the transport layer for processing

Transport layer: the first message that is put into the TCP package and given to the TCP package is processed by the network layer

Network layer: encapsulates the IP packet, gives the IP header, and leaves it to the network interface layer for processing.

Network interface layer: MAC encapsulation, bit stream transmission

3. Corresponding hierarchical relationship of network model

OSI layer 7 protocol is only a reference model, which describes all aspects of network publishing in too much detail. In actual production, it is TCP/IP protocol.

2. Network layer: IP protocol

1.IP protocol

(1) IP protocol version

IPv4:32bits is divided into four segments, represented by dotted decimal, 8bits.8bits.8bits.8bits

Each 8bits is identified by the number 0-255,

00000000.00000000.00000000.000000000.00000000 = "0.0.0.0"

11111111.11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111

IPv6:128bits binary

(2) IP (Internet protocol) address: network number + host number

In the same physical network segment, the IP of the host has the same network number and has a unique host number; the host number of the host in the same network segment cannot be the same.

Note:

1) within the same network segment, the network number remains the same and the CVM number cannot be duplicated.

2) all 0 is the address of the entire network segment, and all 1 is the broadcast address

(3) IP address classification:

Category A:

The first segment is the network number, and the last three segments are the host number

Network number: 0000 0000-0111 1111

Number of networks: 126127

Number of hosts per network: 2 ^ 24-2

Default Subnet Mask: 255.0.0.0Gramplash 8

It is used to perform bit-by-bit "and" operation with IP address to get its network address.

1.3.2.1max 255.0.0.0 = 1.0.0.0

1.3.2.1Compact 255.255.0.0 = 1.3.0.0

Private address: 10.0.0.0Universe 255.0.0.0

Category B:

The first two segments are network numbers, and the last two segments are host numbers.

Network number: 100 0000-10 11 1111 purl 128-191

Number of networks: 2 ^ 14

Number of hosts per network: 2 ^ 16-2

Default Subnet Mask: 255.255.0.0Grample 16

Private address: 172.16.0.0-172.31.0.0

Class C:

The first three segments are the network number, and the last segment is the host number

Network number: 1100 0000-11011111119223

Number of networks: 2 ^ 21

Number of hosts per network: 2 ^ 8-2

Default subnet mask: 255.255.255.0, / 24

Private address: 192.168.0.0-192.168.255.255

Class D: the vulgar public of multicast

1110 0000-1110 1111 purl

Class E: reserved

240-255

Summary:

Class A:0.xx.xx.xx ~ 127.xx.xx.xx, private address 10.0.0.0 ~ 10.255.255.255

Class B:128.xx.xx.xx ~ 191.xx.xx.xx, private address 172.16.0.0 ~ 172.31.255.255

Class C:192.xx.xx.xx ~ 223.xx.xx.xx, private address 192.168.0.0 ~ 192.168.255.255

Class D:224.xx.xx.xx ~ 239.xx.xx.xx

Class E:240.xx.xx.xx ~ 255.xx.xx.xx

Note: Loopback IP network segment

The lo network was originally used as a network for testing the internal loops of the operating system, and it can also provide services that already need to use network interfaces within the system. It is an internal circular network and does not need to install a network card. Its address number is 127.0.0.0 IP 8, and the default host localhost is 127.0.0.1.

2.Netmask subnet mask

Divide a large network segment address into smaller network addresses, reduce the number of hosts in the network segment, make it easier to manage and improve broadcast efficiency.

Method: by using one or more host numbers as network numbers, the network numbers are all represented as 1, and all host numbers are subnetted with a 0 identity

The header of the 3.ip message (the number of digits per line is 32bits)

(1) IP Version: declare the version of the ip packet, ipv4, ipv6

(2) the header length of IHL:Internet Header Length,ip message, which records the length of IP header in 4 bytes.

(3) TOS:Type Of Service, type of service, which is defined to identify the priority, delay, transmission volume and reliability of IP packets.

(4) the total length of the Total Length:IP packet, including the header and data portion, denoted by 16 bytes as 0-65535bytes

(5) Identtification: identify information to identify whether a data segment is a data

(6) Flags: special marks R, DF, MF, the content can be marked as "0DM"

DVR 0 means it can be segmented, while 1 means it cannot be segmented.

M 0 indicates that the IP is the last segment, and 1 indicates that it is not the last segment.

(7) Fragment Offset: segment offset, which is used to identify the position of this IP segment in the original IP packet, similar to the role of sequence numbers.

(8) Time To Live: exist time. A maximum of 255times are forwarded. One router at a time is minus one to zero to discard and no longer forward.

(9) Protocol Number: message protocol code (TCP--6, UDP--17, ICMP--1, IP--4... ...), numerical description

(10) Header Checksum: the header check code, which is used to detect whether there is an error in the IP header

(11) Source Address: source IP address

(12) Destination Address: destination IP address

(13) Options: padding bits, including security handling mechanisms, routing records, timestamps, strict and loose source routing, etc.

(14) Data: real data

III. Transport layer: TCP protocol

1.TCP message header

(1) Source Port: source port number

(2) Destination Port: destination port number that identifies a total of 65536 ports from 0 to 65535 by 16-bit bytes

(3) Sequence Number: packet sequence number, TCP data segmentation

(4) Acknowledgement Number: response serial number

Use the serial number and confirmation number when sending a batch of messages at a time, and the first non-confirmation number of the TCP three-way handshake.

(5) Header Length: head length

(6) Reserved: reserved bit (6 bits)

(7) Code:control Flag, mark control code

This field consists of six bits, and each bits identifies a meaning to indicate the status of the connection and the main actions of the receiver to connect to the packet.

URG (Urgent): 1 is identified as an emergency packet, which needs urgent processing at the receiver, and the Urgent Pointer field will also be enabled.

ACK (Acknowledge): 1 is expressed as a response packet and is related to Acknowledeg Number

PSH (Push Function): 1 means that the other party is required to send other corresponding packets in the buffer immediately without waiting for the buffer to be full.

RST (Reset): 1 indicates that the connection is forced to end and the sender has been disconnected

SYN (Synchronous): 1 indicates that the sender wants both parties to establish synchronous processing (requires establishing a connection) and actively wants to connect to each other.

FIN (Finish): 1 indicates the end of the transfer

(8) Window Size: the window slides to control the flow of data packets. 0 indicates that the buffer is full, so data transmission should be suspended.

(9) TCP Checksum: confirmation check code

(10) Urgent Pointer: emergency data

(11) Options: filled bits, variable length, not used in most cases

(12) Data: data

Three-way handshake Mechanism of 2.TCP Protocol

Three confirmation actions that Three-way handshake:TCP must pass before establishing a connection

(1) the first stage: packet initiation

1) randomly access ports greater than 1024 to monitor for communication with applications

2) TCP header: SYN=1, indicating a request to establish a connection, actively connecting to the other party

3) TCP header: Sequence Number (Client) records the sequence number of the connection packet sent to the server for the first time

(2) the second stage: packet reception and confirmation of packet transmission.

1) the server receives the data packet and acknowledges the received packet

2) echo packet: in the TCP header

SYN=1,ACK=1, indicating an active connection and a response packet

Acknowledgement Number (Service) = Sequence Number (Client) + 1, confirm the use to the client

A new number for Sequence Number (Service), which is used to confirm that the client can indeed receive packets from the server.

3) wait for the client to respond

(3) the third stage: echo acknowledgement packet

1) confirm whether the Acknowledgement Number (Service) received by the message is Sequence Number (Client) + 1

2) send data again: ACK=1,Acknowledgement Number (Client) = Sequence Number (Service) + 1

(IV) Phase IV: obtaining final confirmation

Server-side verification

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