What is a firewall? What role can firewalls play?

　　 One 、 What is a firewall ?

　　 Firewall is a device used for network security , Used to monitor incoming and outgoing network traffic ,( Decide whether to allow or block network traffic according to a set of predetermined security rules ). You can deny access to unauthorized traffic , And allow legal traffic to reach the destination . Firewalls can also prevent malware from accessing your computer .

　　 Two 、 The function of firewall

　　 Firewall has a very good protection . If an attacker wants to reach the target computer , The premise is that we must cross the security line of the firewall . Setting up a firewall can reduce or eliminate unwanted network connections and increase the free flow of legitimate traffic . Firewall is an important supplement to infrastructure , Because they can help connect computers and servers with Internet Isolate , So as to provide data security and privacy . As mentioned earlier , They not only monitor the traffic in and out of your server , And in some cases, it will limit the flow .

　　 3、 ... and 、 How Firewalls Work ?

　　 Firewall monitors all data traffic , To allow good data and prevent bad data according to preset rules . It uses one or any combination of the following three methods ： Packet filtering 、 Status check and proxy services .

　　 Packet filtering method Implemented to monitor network connections . Packets are packed data units that are transmitted along a given network path . Analyze the package and compare it with the configuration rules or “ Access list ” Compare . then , The firewall determines what is allowed or denied access to your environment .

　　 Status check method Allow according to the status 、 Port and protocol analysis traffic patterns . The firewall monitors the activity on the connection from open to closed . It tracks known trusted packets , To determine the authorized data from the website or application and any data from hackers or other website security vulnerabilities .

　　 Agent service method Can prevent Internet Direct network connection between traffic and servers . This type of implementation takes state checking a step further . The firewall acts as an intermediary between your server and the requests made by end users . Check the entire packet , And prevent or allow according to the rule set .

　　 Four 、 Firewall can be used to defend DDoS Do you ?

　　 suffer DDoS When the attack , Malicious traffic will inundate your website , And may cause the server of the target website to crash . A properly configured firewall can help protect your environment from such situations . You can filter the traffic and search for patterns that point to abnormal situations where the attack is in progress . But most DDOS It simulates real user data , Firewalls may not detect , And the server with firewall can only prevent small traffic , Real large flow flood DDOS Attack , The firewall will immediately run out of system resources , unbearable . So I want to ensure the stable operation of the server , You can also try other defense methods . For example, advanced anti DDoS IP、 Advanced anti DDoS server, etc , For defense DDoS and CC Compound attacks are more defensive .