1. What is Squid?
Squid is a software used to buffer Internet data. It does this by accepting requests from objects that people need to download and handling those requests appropriately. That is, if a person wants to download a web page, he asks Squid to get the page for him. Squid then connects to a remote server (eg: http://squid.nlanr.net/) and makes a request to this page. Then, Squid explicitly aggregates the data to the client machine and makes a copy at the same time. The next time someone needs the same page, Squid can simply
Read it from disk, so the data is immediately transferred to the client. Current Squid can handle protocols like HTTP, FTP, GOPHER, SSL and WAIS. But it can't handle things like POP, NNTP, RealAudio and others.
2. What system does Squid run on?
Squid runs on most Unix and OS/2 versions and is known to work:
Windows,AIX，Digital Unix，FreeBSD，HP-UX，Irix，Linux，NetBSD，Nextstep，SCO，Solaris
3. Definition of various Squid agents
forward proxy
a. Standard proxy cache server
A standard proxy caching service is used to cache static web pages (eg, html files and image files, etc.) to a host (ie, a proxy server) on the local network. When the cached page is accessed for the second time, the browser will directly obtain the request data from the local proxy server instead of requesting data from the original web site. This saves valuable network bandwidth and increases access speed. However, to do this, the proxy server's IP address and port number must be explicitly specified on each internal host's browser. When the client surfs the Internet, each time the request is sent to the proxy server for processing, and the proxy server determines whether to connect to the remote web server to obtain data according to the request. If there is a target file in the local buffer, you can directly transfer the file to the user. If not, retrieve the file first, save a buffer locally, and then send the file to the client browser.
b. Transparent Proxy Cache Server
The transparent proxy buffer service and standard proxy server function exactly the same. However, the proxy operation is transparent to the client's browser (ie, it is not necessary to specify the IP and port of the proxy server). Transparent proxy servers block network traffic and filter out HTTP (port 80) traffic to the outside world. If the client's request is buffered locally, the buffered data is sent directly to the user. If there is no local buffering, the request is sent to the remote web server. The rest of the operations are exactly the same as the standard proxy server. For Linux operating systems, transparent proxies are implemented using Iptables or Ipchains. Transparent proxies are especially useful for ISPs (Internet Server Providers) because no browser settings are required.
Reverse proxy:
a. Reverse proxy cache server
A reverse proxy is a proxy service that is completely different from the first two proxies. Use it to reduce the load on the original WEB server. The reverse proxy server undertakes the request for the static page of the original WEB server, preventing the original server from being overloaded. It is located between the local WEB server and the Internet, handles all requests to the WEB server, and organizes the direct communication between the WEB server and the Internet. If the page requested by the Internet user is buffered on the proxy server, the proxy server sends the buffered content directly to the user. If there is no buffering, first send a request to the WEB server, retrieve the data, cache it locally, and then send it to the user. This method reduces the load of the WEB server by reducing the number of requests to the WEB server.