What is the URL

URL is a Uniform Resource Locator,

Component of the URL

URL = Protocol + Domain name or IP address + port number [omitted by default] + path + query parameters + anchor point

For example: baike.baidu.com/search?word…

  • Protocol: HTTPS
  • Domain name: baike.baidu.com
  • Port: The default port is 443
  • Path: / ssearch
  • Query string:? word=123&pn=0&rn=0&enc=utf8
  • Anchor: # 1

agreement

HTTP uses port 80 by default, and HTTPS uses port 443 by default

The domain name

A domain name is an alternate name for IP.

  • A domain name can have multiple IP addresses (this is called load balancing to prevent one machine from becoming overwhelmed)
  • One IP can have different domain names (this is called shared hosting, for poor developers)

IP related

  • An IP address can locate a device
  • IP is divided into external IP (router at home) and internal IP (mobile phone and computer).
  • Devices on the Intranet can access each other, but cannot directly access the Internet
  • An Intranet device needs to access the Internet through a router
  • Devices on the extranet can access each other, but cannot directly access the Intranet
  • The extranet also needs to access the Intranet through a router
  • ping baidu.comCan you check what domain name corresponds to what IP, and the website latency

IP addresses are classified into external IP addresses and internal IP addresses

Special IP address

  • 127.0.0.1 indicates itself
  • Localhost specifies itself by host
  • 0.0.0.0 does not indicate any device

Domain classification

  1. The first level is the top-level domain, which includes generic top-level domains such as.com,.net, and.org. And country and region top-level domains, such as.us,.cn, and.tk
  2. Baidu.com is a secondary domain name
  3. www.baidu.com is a level 3 domain name

So www.baidu.com and Baidu.com are two domain names. IO is the domain name of github, and userid.github. IO is the domain name of each user

The port number

A server can provide many services, and each service has a different number. This number is the port.

  • Port 80: HTTP service
  • Port 443: HTTPS service
  • 21 Port: FTP service

Port usage rules

  1. Ports 0-1023 are for system use. We generally use ports after 1024
  2. For example, http-server uses port 8080 by default
  3. If one port number is occupied, other ports must be used
  4. Different ports can be specified with the -p argument, for example, port 1023 can be specified
http-server -c-1 -p 1023
Copy the code

The path

How to request different pages on the same server? Paths are not necessarily suffixed developer.mozilla.org/zh-CN/docs/… Developer.mozilla.org/zh-CN/docs/…

Query parameters

Can I request the same page and get different content? Query parameters www.baidu.com/s?wd=hi www.baidu.com/s?wd=hello

The anchor

Same content, different location? Use the anchor point developer.mozilla.org/zh-CN/docs/… Developer.mozilla.org/zh-CN/docs/… Note that anchors do not support Chinese, they will be encoded in Chinese. # Reference books will become #%E5%8F%82%E8%80%83%E4%B9%A6 Anchors cannot be seen on the network because they are not transmitted to the server

DNS

DNS is the abbreviation of Domain Name System (DNS). It consists of a Domain Name server (DNS) and a Domain Name server (DNS). Domain names correspond to IP addresses through DNS

How to find the corresponding IP address by domain name

  • Nslookup + Domain name such as nslookup baidu.com How many IP addresses can be found