The first stage of the exercises: Python basic programming foundation to develop the knowledge base day31 network of small exercises

day31 Homework

1. Class 5 talk network protocol layer model, the contents of each sort out

Physical Layer

Physical layer functions: main transmitting low voltage (electric signal) based on the electrical characteristics, a high voltage corresponding to the number 1, a low voltage corresponding to the digital 0. Network data is transmitted through the electrical signals consisting 01010101100101 format.

data link layer

The electrical physical layer packet, a set of electrical signals constitute a data packet, called 'frames', each data frame is divided into: a header and a data head data of two parts.

• fixing head comprising :( 18 bytes)
  • Sender / source address of 6 bytes
  • Recipient / destination address, six bytes
  • Data type, six bytes
• 46 byte data comprising :( minimum, maximum 1500 bytes)

mac address: datagram sender address and the recipient address is mac address. Each one has a unique network card mac address: 12 hexadecimal number (first 6 digits is the vendor ID, the line number is 6)

Broadcasting: communication within the same LAN, thanks to roar, to send data to a computer local area network, you need to send a request to all the computers, and then we have to get that computer to receive data. (Bulk)

Network layer

• ip: ipv4: 32-bit binary represented: dotted decimal notation from 0.0.0.0 to 255.255.255.255, the range is limited, not shown all the network devices, so there ipv6
• Subnet Mask: subnet mask and ip is determined by two ip is in the same network segment, do a bitwise ip address and subnet mask by
• ip have a relationship with mac converter
  • Host 172.16.10.10/24 access 172.16.10.11/24
    • ARP protocol: send a broadcast packet, the destination hosts mac address
    • mac address learning: mac address and ip address mapping table
    • The first one will be added to the received data ip / mac mapping table { '172.16.10.1': 'localhost'}
    • Any kind of protocol has headers and content

Transport Layer

• tcp protocol:
  • Three-way handshake, four wave (focus, Figure), how the connection is established, how to send data to ensure reliable, disconnect how to disconnect, there is a state in the process of establishing a connection
  • If you see a large number of state services syn_rcvd
  • dos and ddos ​​attacks: denial of service attacks, distributed denial of service attack
  • Port number: port range 0-65535,0-1023 port is occupied by the system
• udp protocol:
  • Transmitting, to not require a response, not on the data, (see video)
• port
  • Ip + subnet mask uniquely determined by a device
  • Subnet mask by ip + CD + port number uniquely identifies a software
• Semijoin pool

Application layer

The origin of the application layer: the user is using the application, are working at the application layer, is the development of the Internet, everyone can develop their own applications, a variety of data, data must be provided in the form of good organization

Application layer functions: a predetermined data format of the application.

• Example: TCP protocol data can be transferred to various programs, such as Email, WWW, FTP and the like. So, there must be agreement provides different e-mail, Web pages, FTP data format, these application protocols constitute the "application level."

2. The three-way handshake described drawing, four wave, and c are end and side state s

Three-way handshake:

• The client sends a connection request to the server.
• Responses Agree server the client's request and sends a connection request from a client.
• Client server response, agreed to connect.

Four wave:

• The client sends a disconnection request to the server.
• Agreed to request the server to respond to client disconnected.
• The server sends a request to disconnect customers.
• The client agreed to respond to service requests end disconnected.

3. Write a client to achieve the string hello world send to the server, write a server, the client sends the data into a capital return

Server code:

import socket

soc = socket.socket(socket.AF_INET,socket.SOCK_STREAM)

soc.bind(('127.0.0.1',8081))
soc.listen(5)
conn,addr = soc.accept()
print(addr)
data = conn.recv(1024)

conn.send(data.upper())
conn.close()

Client code:

import socket
soc = socket.socket()

soc.connect(('127.0.0.1',8081))

soc.send(b'hello world')

data = soc.recv(1024)

print(f'我收到了服务端回的消息:{data.decode("utf8")}')

soc.close()

operation result:

I received a message back to the server: HELLO WORLD

blog address

https://www.cnblogs.com/foreversun92/