URL

  • Chinese name: Unified Resource Positioning system
  • Uniform Resource Locator
  • URL definition: A representation on the Internet’s World Wide Web service used to specify the location of information

Composition: Protocol + domain name + port + path + query parameters + anchor

  1. Protocol: Specifies the transport protocol to use. The most common is HTTP.

    • File: A resource is a file on the local computer. The format is file:///, followed by three slashes.
    • FTP: Accesses resources through FTP. Format: FTP://
    • HTTP: Access the resource through HTTP. Format: HTTP://
    • HTTPS: access the resource using secure HTTPS. Format: HTTPS://

  2. Hostname: indicates the hostname or IP address. The hostname can contain the username and password required for connection (format: username:password@hostname).

  3. Port: A computer has 65535 ports, among which ports 0 to 1023 are used by the system. Each transport protocol has a default port number. For example, HTTP has a default port number of 80. If omitted, the default port number is used.

  4. Path: A string separated by a slash (/) to indicate the address of a directory or file on a host.

  5. Parameters: Optional for specifying parameters.

  6. Query (query) : An optional parameter passed to a web page. Multiple parameters can be separated by ampersand, and the name and value of each parameter are separated by an =.

  7. Fragment: STRING used to specify the label on a web page. For example, if there are multiple definitions in a web page, you can use fragment (#) to locate a particular definition.

DNS

  • The domain name system
  • English: Domain Name System, abbreviation: DNS
  • As a distributed database that maps domain names and IP addresses to each other, it enables people to access the Internet more conveniently.

Nslookup: domain name query command

  • Usage example: nslookup www.baidu.com
  • Domain name query refers to query the WHOIS registration information of a domain name. When using a domain name to surf the Internet, users want to learn more about the domain name and name server, which uses WHOIS. WHOIS is a search engine linked to a domain name database. Generally speaking, WHOIS is one of the name services provided and maintained by the Network Information Center (NIC).

What is the function of IP? How does the ping command work

  • Short for Internet Protocol
  • It is the core of the entire TCP/IP protocol family and constitutes the foundation of the Internet
  • 0.0.0.0 represents the address of this host, which can be used by any host on the network to represent itself
  • Any IP address that begins with the number 127 (127.x.x.x) is called a loopback address. It is a reserved address, most commonly represented as 127.0.0.1.
  • There is an interface on each host corresponding to IP address 127.0.0.1, called the loopback interface. The IP protocol states that when any program uses a loopback address as the destination address, the protocol software on the computer does not send the datagram to the network, but returns the data directly to the local host. Therefore, the data packet whose network id is 127 cannot appear on any network, and the host and router cannot broadcast any path finding information for this address. Echo addresses are used to test native network protocols or to communicate between local processes.

Ping:

  • It is used to determine whether the local host can successfully exchange (send and receive) packets with another host. Based on the returned information, you can infer whether the TCP/IP parameters are set correctly, whether the operation is normal, and whether the network is normal.
  • Example Ping www.baidu.com

The domain name

  • English: Domain Name, also known as the Domain Name
  • The name of a computer or computer group on the Internet, consisting of a series of dotted names, used to identify the location (and sometimes geographical location) of the computer during data transmission
  • Because IP addresses are not easy to remember, people design domain names, and use DNS to map domain names and IP addresses to make people access the Internet more conveniently.

Types of domain name

  • Top-level domain name:

.net- formerly used by Internet service providers, now unrestricted. Org – formerly used by organizations that do not fall into other generic top-level domain categories, now unrestricted. Edu/.gov /- for US educational institutions/US government agencies

  • Secondary domain name:

The field closest to the left of the top-level domain name. For example, in zh.wikipedia.org, Wikipedia is a secondary domain name

  • Level 3 Domain name:

That is, the field closest to the left of the second level domain name, from right to left can have four level domain name, five level domain name and so on. www.ncic.ac.cn, where the WWW prefix indicates that this domain name corresponds to the World Wide Web service, each level domain name is divided by English half period, “NCIC” as a level 3 domain name is the subdomain name of “ac.cn”.