Overview of proxy servers

1. What is a proxy server?

The Proxy Server stands for Proxy Server. Its function is to obtain network information from the Proxy network user. It is a transfer station for network information.

In general, when we use a web browser to directly connect to other Internet sites to obtain network information, we need to send a Request signal to obtain the answer, and then the other Party sends the information back in bit mode. The proxy server is a server between the browser and the Web server. With this server, the browser does not directly go to the Web server to retrieve the Web page, but sends a request to the proxy server, the Request signal will be sent to the proxy server first. The proxy server will retrieve the information required by the browser and send it to your browser. In addition, most proxy servers have the buffer function, which is like a large Cache, which has a large storage space and constantly stores new acquired data in its local memory, if the data requested by the browser already exists and is up-to-date on its local memory, it will not retrieve data from the Web server again, directly transfer the data in the memory to the user's browser, which can significantly improve the browsing speed and efficiency.

More importantly, the Proxy Server is an important security function provided by the Internet link-level gateway. It mainly works in the Open System Interconnection (OSI) the dialog layer of the model.

Ii. Proxy Server Classification

1. HTTP proxy is classified by anonymous function.

Whether the IP address can be hidden.

Non-anonymous proxy: The agent does not have the anonymous function.

Anonymous proxy. When using this proxy, although the accessed Website Cannot know your IP address, you can still know that you are using the proxy, and some web pages that detect IP addresses can still find your IP address.

Highly anonymous proxy: when using this proxy, the accessed website does not know your IP address, or you are using a proxy for access. The hidden IP address of this proxy is the most powerful.

2. Security Classification Based on request information

Full anonymous proxy: does not change your request fields (Message), so that the server looks like a real client browser accessing it. Of course, your real IP address is hidden. The server's network management does not think you are using a proxy.

Normal anonymous proxy: it can hide your real IP address, but it will change your request fields. It may be considered as a proxy, but it is only possible. Generally, it is okay. But do not be misled by its name. Its security may be higher than that of all anonymous proxies. Some proxies may strip some of your information (like the stealth mode of the firewall ), this prevents the server from detecting your operating system version and browser version.

Elite agent: The agent is more anonymous and can hide information about systems and browsers. This type of proxy is highly secure.

Transparent proxy (simple proxy): a transparent proxy means that the client does not need to know the existence of a proxy server. It adapts your request fields (Message) and sends a real IP address. Note: The encrypted transparent proxy is an anonymous proxy, which means you do not need to set proxy, for example, the Garden 2 program.

3. Classification by proxy server usage

1) Http Proxy: the proxy client accesses the webpage through the main proxy browser. Its ports are generally 80, 8080, and 3128.

2) SSL Proxy: supports up to 128-bit http proxy for encrypted websites. An encrypted website is a website starting with https. The standard ssl port is 443.

3) http connect Proxy: allows you to establish a TCP connection to a proxy server on any port. This proxy can be used not only for HTTP, but also for FTP, IRC, and RM Stream Services.

4) FTP Proxy: the ftp software on the proxy client accesses the ftp server. The ports are generally 21 and 2121.

5) POP3 Proxy: the mail software on the proxy client uses pop3 to receive mails. The port is generally 110.

6) Telnet proxy: This proxy can be used for remote control and frequent intrusion. The port is generally 23.

7) Socks Proxy: it is an all-around proxy, just like a patch board with many Jumpers. It simply connects one end of the system to the other end. Supports multiple protocols, including http, ftp, and other types of requests. Socks 4 supports socks 4 and socks 5. socks 4 only supports TCP protocol, socks 5 supports TCP/UDP protocol, and various authentication mechanisms. The standard port number is 1080.

Socks proxy is a common proxy server that uses the socks protocol. Socks is a hierarchical underlying gateway developed by David koblas in 1990. It has been an open standard for Internet RFC standards since then. Socks does not require applications to follow a specific operating system platform. Socks proxy is different from the application layer proxy and HTTP layer proxy. Socks proxy simply transmits data packets, you don't have to worry about the application protocols (such as FTP, HTTP, and NNTP requests ). Therefore, Socks proxy is much faster than other application-layer proxies. It is usually bound to port 1080 of the proxy server. If you are on a corporate network or campus network, you may need to use SOCKS to access the Internet through a firewall or proxy server. Generally, dial-up Internet users do not need to use it. Note: The proxy server used to browse webpages is usually a special http proxy, which is different from SOCKS. Therefore, browsing a webpage does not mean that you can access the Internet through SOCKS. Common firewalls or agent software support SOCKS, but the administrator needs to enable this function. If you are not sure whether SOCKS is required or whether SOCKS is available, contact your network administrator. To use socks, you need to know the following:

① SOCKS Server IP Address

② SOCKS service port

③ Does SOCKS service require user authentication? If necessary, you need to apply for a user and password from your network administrator

With the above information, you can enter the information in "network configuration", or enter the information in the first registration, you can use the socks proxy.

In practical applications, SOCKS agents can be used as: email, newsgroup software, network call ICQ, online chat MIRC, and the use of proxy servers to play games, among other game applications.

8) TUNNEL Proxy: Packets converted by the HTTPTunnet program are encapsulated into http requests to penetrate the firewall, allowing the HTTP server to do anything TCP can do. The function is equivalent to Socks5.

9) Document agent: it can be used to query database agents. Through these agents, you can obtain database resources related to scientific research on the Internet, such as querying the Sciencedirect website (SD), Academic Press, IEEE, SPRINGER, and other databases.

10) Education Network Proxy: the LAN of an academic education institution allows computers without the permission to go abroad or access a certain IP segment to access relevant resources through a specific proxy server.

11) stepping stone Proxy: it can be used as a special socks5 proxy with dynamic encryption and can be directly used in PSD software. Generally, the port is 1813.

12) Ssso Proxy: The ssso program on the proxy client accesses the remote website. It has a super proxy with SSL encryption strength and supports socks.

13) Flat Proxy: The flatsurfer program on the proxy client accesses a remote website. It has a special proxy with high-strength encrypted data streams. socks is supported. A maximum of three sub-links can be set and a traversal proxy can be set. Generally, the port is 6700.

14) SoftE Proxy: The SoftEther program on the proxy client accesses a remote website. It uses the virtual HUB and virtual network card technology, and has VPN functions and multiple authentication methods for proxy. It complies with the https protocol.

Iii. Main Functions of the proxy server

In general, the proxy server has the following functions for common Internet users (some advanced functions are not mentioned, because they may not be used ):

1. connect to the Internet and the Intranet to act as a firewall: Because All Intranet users access the outside world through a proxy server, only one IP address is mapped, so the outside world cannot directly access the Intranet; at the same time, you can set IP address filtering to restrict Intranet access to external networks. In addition, two Intranets without interconnectivity can also exchange information through third-party proxy servers.

2. Saving IP Overhead: As mentioned above, all users only occupy one IP address, so they do not need to lease too many IP addresses to reduce network maintenance costs. In this way, many machines in the local area bureau that are not connected to the Internet can connect to the Internet through an intranet proxy server, greatly reducing the cost. Of course, it also has its disadvantages. For example, many network hackers hide their real IP addresses in this way and escape monitoring.

3. Use it to speed up the browsing of some websites: Sometimes we access some foreign or Hong Kong and Taiwan websites, which is as slow as snails, but as long as you choose the proxy server correctly, the speed can be improved. Sometimes the speed improvement is obvious! The bandwidth itself is small, and the proxy with a large bandwidth is connected to the target host. In addition, the proxy server usually sets a large hard disk buffer (which may be several GB or larger). When external information passes, it is also saved to the buffer, when other users access the same information again, the information is directly retrieved from the buffer and transmitted to the user, thus improving the access speed.

4. Through it, we can access some websites that we can't visit at ordinary times: If you don't believe it, you can open your browser immediately and enter the URL "www.geocities.com. How? You don't have to wait for the browser here. It's not that your network speed is slow or you don't have this website, but that you cannot access it (there are many of these types of websites on the network ). Why can't I access it? This is a problem... there are many kinds of arguments, most of which say that the domestic network is restricted to access, so some websites cannot go. If you have seen the above situations in the previous browsing process, it seems necessary to try to use the proxy server. How can I access these websites? Please continue reading this series of articles!

References: http://www.linkwan.com/gb/tech/sysinte/05091102.htm

References: http://www.linkwan.com/gb/tech/sysinte/05091102.htm