502BadGateway

葫芦狠狠瞪了他一眼，道：别胡说。L PM2.5 dust, toxic smoke and water sourcesWhen a client accesses a server's web service, The client sends a message to the network card, The tcp/ip stack is part of the kernel, Therefore, the client information is transferred to the web service in user space through the kernel's TCP protocol, At this time, the destination destination of the client message is on the socket (IP: Port) that the web service is listening for. When a web service needs to respond to a client request, The destination destination of the response message sent by the web service is the client, At this time, The IP and port that the web service listens on becomes the origin instead, As we said, Netfilter is the real firewall, It is part of the kernel, Therefore, if we want the firewall to achieve the goal of "fire prevention", You need to set up checkpoints in the kernel. All incoming and outgoing messages have to pass through these checkpoints. After checking, those that meet the release conditions can be released, while those that meet the blocking conditions need to be blocked. As a result, input checkpoints and output checkpoints appear. These checkpoints are not called "checkpoints" but "chains" in iptables.五只终日脏兮兮的小狗因为贪食冰淇淋被飞机从华盛顿带到了阿拉斯加，起初，它们面对满山冰雪异常兴奋，但很快便被寒冷的天气打败。这时，它们认识了一只爱斯基摩犬，并通过它知道了一个故事。