This article makes the computer "firewall" easy to understand.

Latest update time：2021-05-09

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This article will give a detailed explanation of the firewall technology often mentioned in computer networks in the form of illustrations and easy-to-understand language , aiming to let readers know and understand the "story" of firewalls and reduce more computer blind spots!

1. Why do you need a firewall?

While the Internet is accelerating the process of global informatization, it also poses severe challenges to information security around the world. The openness and freedom of the Internet have brought great convenience to humans in accessing and publishing information, but this is also the main reason why Internet information is easily contaminated, invaded and destroyed. These damages mainly come from the following aspects:

❶The Internet trusts all access hosts

The openness of the Internet allows any network device in the world to access the Internet without testing the reliability of the device . That is to say, if there is a device with weak security and reliability among all the hosts connected to the Internet, as long as this device is broken, If a host is installed, any harmful data or viruses can enter the Internet through the host, affecting more Internet devices, causing immeasurable losses to global companies and individuals, and causing unpredictable disasters.

❷Imperfect various protocol services

All services used on the Internet today, such as Telnet services, DNS services, FTP services, Web services, ActiveX, etc., have security vulnerabilities. The patches we often apply to computers include the function of repairing these services. Any vulnerability in these services can become a breakthrough for Internet hosts to be attacked and destroyed!

❸ Security risks of TCP/IP protocol

The TCP/IP protocol is an international information standard that must be followed when any two hosts on the Internet communicate. However, because the TCP/IP protocol is completely open and is not a set of information rules with complete security, it has become a method for criminals to implement. One of the key targets of cyber attacks. The security issues of the TCP/IP protocol mainly include the following points:

The TCP/IP protocol focuses on establishing a network connection and taking full consideration of connection security.

The TCP/IP protocol is based on IP addresses, and address-based protocols themselves have various security issues.

Host communication on the Internet only recognizes IP messages, and messages can be intercepted or modified by criminals. This cannot guarantee that all Internet hosts come from a trustworthy network environment, which greatly reduces the difficulty of network attacks by criminals.

The Internet itself has loopholes

Since all application layer computer programs transmit data through TCP connections, as long as TCP security vulnerabilities are exploited, attackers can directly remotely control the target host to pollute/steal data, intercept passwords, damage computers, etc., so The TCP/IP protocol cannot guarantee the absolute security of the network.

When encountering the above problems, tracing the root cause is very difficult because the Internet trusts every device connected to it, the device can come from anywhere with Internet access, and can use any service vulnerability or TCP/ Vulnerabilities in the IP protocol.

Difficult to find attack source host

In this case, it is almost impossible to solve the problem of the target host being compromised through the source, because the workload to prevent all types of Internet attacks is impossible, but conversely, it is feasible to control only the Internet data entering the target host Yes, this requires a network security solution that can control data access between a safe network environment and an unsafe network environment. To achieve this goal, the most basic solution is firewall technology!

2. The function of a firewall - is it fire prevention?

The term firewall has the same name as a car component. The function of the firewall in the car is to isolate the passengers from the engine to prevent the car engine from catching fire and spreading to the passengers. In addition to automobile firewalls, there is also the concept of firewalls in real buildings . In the construction field, the role of firewalls is to block the source of fire and prevent the spread of fire.

From the above content, it can be concluded that the function of a firewall is indeed fire prevention. However, in the computer field, a firewall prevents another kind of "fire" - all insecure factors on the Internet. What it blocks is the "fire" in enterprises, Contagion within an agency or organization’s internal network!

Computer firewalls are also "fireproof"

As a set of network security management mechanisms, firewalls can isolate the network that needs to be protected from the open Internet or other untrustworthy network environments, making the protected network a fully controllable, trustworthy and secure network . This is the firewall. Main functions!

3. The true face of a firewall—is it really a wall?

We have already introduced the reason for introducing firewalls : to solve the various network security vulnerabilities mentioned in the previous article! So, what does a firewall really look like? Is it really a wall? How is the firewall implemented? This section reveals it for you!

Uncover the true face of firewalls

Engineers from AT&T defined the specifics of a firewall:

◆ All data exchange between the internal network and the external network must pass through the firewall

◆ All intranet access communications must be authorized by the firewall

◆ The entire intranet system has strong reliability

From a definition point of view, a firewall is a "thing" that can control network data entering and exiting the internal and external networks. It can not only check network data, but also has the ability to protect the internal network from external unsafe factors. Therefore, in terms of function, a firewall is a centralized A device that integrates isolation and review; in terms of implementation, a firewall is a host or router system composed of a set of hardware devices (routers, hosts, etc.) located in a special network location.

Firewall = Function-specific host/router

4. Ideal Firewall Structure

Before introducing the firewall structure, we must first understand three concepts:

Intranet - also known as internal network area, refers to the enterprise's internal network or part of the internal network
External network - also known as external network area, refers to the Internet or non-internal area network, which is not a network environment trusted by the Internet
Border network - a subnet accessible from both internal and external networks
Filtering router - the simplest firewall formed by setting relevant filtering functions in ordinary routers
Proxy server - acts as a gateway for intranet DNS , intranet and external network communication, and can provide various information services (mail, ftp services, etc.)

★ The ideal firewall structure is as follows:

Ideal firewall structure

As can be seen from the above figure, the ideal firewall distributes multiple service functions (WWW/FTP/MAIL, etc.) of one host to multiple independent slave hosts for separate management. There are three lines of security defense in an ideal firewall. The first line of defense is the filtering router, which can filter IP packets; the second line of defense is the single-service hosts scattered in the border network (the proxy server in the picture) , since only one service is provided, on the one hand, it makes the hosts in the border network easier to configure, on the other hand, it increases the difficulty of the internal network being breached; the third line of defense is the internal router, which is the last means of security protection for the internal network.

In fact, today's commercial firewalls have integrated all the above functions into a single product. They only need to be configured to achieve similar functions in the above ideal structure. For example, a firewall product from Huawei:

A firewall product from Huawei

5. How to use window firewall to block software from connecting to the Internet? ——Just a few steps to set up

When we use computers to study and work, we often encounter such a problem: we want to prohibit a certain software from connecting to the Internet for various reasons, but we don’t know what to do:

For example, the cracked software automatically updates in the background, causing the crack to fail.
For example, some illegal software automatically downloads and installs other junk software
For example, some malicious software often pops up advertisements
...

When encountering the above problems, we can use the firewall that comes with the window system to prohibit these software from connecting to the Internet to avoid various problems. We will show readers the specific operations directly through screenshots:

Windows firewall prohibits software networking process