Soft test (software designer) test site summary: https://blog.csdn.net/Lzy410992/article/details/117321579
OSI/RM seven-layer model
Example:
Answer: B, the router is on the third layer (network layer) and cannot pass.
Broadcast domain and collision domain: A
hub connects a host to form a collision domain, and no port of a switch belongs to a collision domain; a router connects to a network to form a broadcast domain.
Network Technology Standards and Protocols
Layer 2 protocol:
ICMP Internet Control Protocol (ping) : Used to transmit messages about communication problems, such as datagrams not reaching the destination station, routers not having enough cache space, etc. ICMP packets are encapsulated in IP datagrams for transmission, and reliable delivery is not guaranteed.
ARP Address Resolution Protocol: IP => MAC, RARP Reverse Address Resolution Protocol: MAC => IP
PPP Point-to-Point Protocol: Can support multiple authentication mechanisms and allow the use of back-end servers to implement complex authentication processes.
Layer 3 protocols:
TCP Transmission Control Protocol: reliable connection, connection establishment with verification mechanism (three-way handshake),
UDP User Datagram Protocol: no connection establishment, unreliable, no connection management capability, not responsible for resending lost or erroneous data messages , without flow control capability.
| TCP three-way handshake | TCP waved four times |
|---|---|
 |
 |
Four-layer TCP-based protocol:
SMTP Simple Mail Transfer Protocol: mainly used to transmit mail. Port: 25, the transmitted mail message needs to be encoded in ASCII.
FTP file transfer : Control port: 21, Data port: 20 (active mode), 1025-65535 (passive mode)
POP3: Post Office Protocol Version 3 : Mainly used to support remote management of emails on the server using the client. The POP3 protocol that provides SSL encryption is called POP3S. Port: 110, using C/S mode for communication, through TCP transmission;
HTTP Hypertext Transfer Protocol
HTTPS Secure Hypertext Transfer Protocol : It is a secure communication channel, developed based on HTTP, for exchanging information between client computers and servers . HTTPS uses Secure Sockets Layer (SSL) for information exchange.
Four-layer UDP-based protocol:
SNMP Simple Network Management Protocol: consists of a set of network management standards, including application layer protocols, database models and a set of resource objects. Packets are encapsulated in UDP.
DHCP Dynamic Host Configuration Protocol: Dynamically assign IP addresses (based on leases), DHCP clients can obtain the local IP address, DNS server address, DHCP server address, default gateway address, etc. from the DHCP server.
DNS Domain Name Resolution Protocol: Converts domain names to IP addresses.
MIME is an Internet standard that extends the e-mail standard to support multimedia data.
HTTP request process:
enter the URL in the browser, the browser sends a domain name resolution request to the DNS server and obtains the result, establishes a TCP connection with the server according to the destination IP address and port number, the browser sends a data request to the server, and the server sends the web page data Send to the browser, the browser parses the received data and displays it, the communication is completed, and the TCP connection is disconnected.
The difference between HTTP and HTTPS:
https needs to apply for a CA certificate. Generally, there are very few free certificates. You need to pay.
http is a hypertext transfer protocol, and information is transmitted in plain text
. Port 443
http connections are simple and stateless.
The https protocol is a network protocol constructed by the SSL+HTTP protocol that can perform encrypted transmission and identity authentication, and is more secure than the http protocol.
Computer commands:
netstat is a console command, a very useful tool for monitoring TCP/IP networks. It can display routing tables, actual network connections, and status information for each network connected device. It is generally used to check the network connection of each port of the machine.
ping is a communication protocol that is part of the TCP/IP protocol. Use the "ping" command to check whether the network is connected, which can help analyze and determine network failures.
ipconfig shows information; ipconfig /all shows details; ipconfig /renew updates all adapters; ipconfig /release releases all connections; ipconfig /flushdns : cleans and resets the contents of the DNS client resolver cache.
msconfig is a system configuration utility. Enter and confirm in the start menu to find the program to enable or disable. It can help the computer to prohibit programs that do not need to be run and speed up the operation of the computer.
The cmd command prompt is a working prompt in the operating system that prompts for command input. The command prompt varies in different operating system environments.
nslookup can specify the type of query, the time to live of DNS records can be found, and which DNS server to use for interpretation can also be specified.
tracert is a traceroute utility used to determine the path an IP packet takes to reach a destination . The Tracert command uses the IP Time to Live (TTL) field and ICMP error messages to determine the route from one host to other hosts on the network.
domain name
URL Basics: A
URL Uniform Resource Locator is a representation of the location and access method of resources on the Internet, and is the address of a resource on the Internet. Every file on the Internet has a unique URL.
URL: protocol://hostname.domain name.domain name suffix or IP address (:port number)/directory/filename
URL: http:/www.baidu.com/channel/hello.html
http:protocol type
www:hostname
baidu.com: domain name
channel: path name
hello.html: file name
Domain name query record: first query the HOSTS table, then query the local DNS cache, and then query the DNS server, followed by the root domain name server, top-level domain name server, and authority domain name server
Example:
Answer: A, the root domain name server does not directly tell the answer to the local domain name server, but the intermediate domain name server directly tells the answer to the local domain name server
Classification of computer networks:
Network Planning and Design
Logical Design:
Physical Design:
Hierarchical Design:
Subnetting
IP address:
IP address = network number + host number
Class A address: the network number is 8 bits, and the highest bit is 0, and the network number is 0 ~ 127.
Class B address: The first two segments are the network number (the first 16 bits) (the fixed highest bit is 1), the last 16 bits are the host number, and a class B address can accommodate 216 - 2 hosts.
Class C address: the first 3 segments are the network number, the latter segment is the host number, a class C address can accommodate 28-2 hosts
Subnet division:
1. Subnet mask
2. Divide a network into multiple subnets (take part of the host number as the subnet number)
3. Combine multiple networks into a large network (remove part of the network number and use it as the host number) )
example:
Subnet division: Use several host bits as subnet numbers to
judge whether two networks belong to the same subnet: Convert their IP addresses to binary, and judge whether the network bits and subnet bits are exactly the same, if they are the same, they are in the same subnet.
The subnet mask for the host route is 255.255.255.255
Uncategorized Addressing:
Example:
The network number has 20 bits, then 12 bits are the host number, and the first 24 bits of class C are the network number, so we can now take 4 out of the address block to divide the subnet, 1111B = 16D, so 16 subnets can be divided.
IP addresses with special meaning:
HTML：
Wi-Fi:
IPV6:
Two IPV6 points can communicate through existing IPv4 addresses, and tunneling technology is required; the communication between pure IPv6 nodes and pure IPv4 nodes needs to use translation technology.
network access technology
Public Switched Telephone Network (PSTN): The most primitive form of dial-up Internet access, Internet access and phone calls cannot be carried out at the same time
Integrated Services Digital Network (ISDN): Internet access and calls can be carried out together.
Asymmetric Digital Subscriber Line (ADSL): telephone line communication, downlink 8M, uplink 512K
coaxial fiber technology (HFC): equal uplink and downlink, the backbone network is optical fiber, the user is coaxial cable (cable TV connection cable)
WCDMA: Wide range of applications, the most mature, the best stability, the best base station.
CDMA2000: operated by China Telecom.
TD-SCDMA (domestic standard): Low speed, high power consumption, operated by China Mobile. Laid the foundation for 4G
The past real questions of the soft exam and related video courseware of station B:
link: https://pan.baidu.com/s/1e4d1-HGOzcEVHSK8Q0j_xA
Extraction code: acij