SYN flood attack how to do? Summary of common emergency treatment methods

in the TCP/IP network architecture, the three-way handshake is the core process of establishing a connection, and the SYN flood attack takes advantage of the vulnerability of this mechanism to launch a malicious attack. When the server encounters a SYN flood attack, it will fail to respond to normal user requests due to the half-connection queue being full, causing service paralysis. This article will summarize the SYN flood attack response plan from the dimensions of attack identification, emergency response, and advanced protection, and help operation and maintenance personnel quickly stop losses and build a long-term defense system.

How to quickly identify SYN flood attacks?

timely and accurate identification is the first step to deal with SYN flood attacks. Only by accurately judging the type of attack can we take targeted measures.

1, monitor semi-connected queue status

view the server semi-connection queue through netstat, ss and other system commands. If the number of connections in the SYN_RECV state is found to far exceed the normal threshold, and the source IP is scattered or concentrated in a specific network segment, there is a high probability of encountering a SYN flood attack. At the same time, it can be combined with CPU and memory usage changes. If the resource occupation is abnormally soaring but the normal request volume is not increasing, it can also be used as an auxiliary judgment basis.

2, analysis of network traffic characteristics

use Wireshark, tcpdump and other traffic analysis tools to capture data packets. If a large number of requests containing only SYN packets are found, and there is no subsequent ACK packet response, and the source IP of the data packet is mostly forged or non-existent addresses, it can be confirmed that it is a SYN flood attack. In addition, the attack traffic is usually characterized by bursts and large traffic, which will occupy a lot of bandwidth resources in a short time.

SYN flood attack basic emergency response

when it is confirmed that the SYN flood attack, the need to immediately take basic disposal means, priority to protect the access rights of normal users, to avoid complete service paralysis.

1, Temporary adjustment of semi-connected queue parameters

modify the system kernel parameters to enlarge the maximum length of the semi-connected queue, such as adjusting the tcp_max_syn_backlog, tcp_synack_retries and other parameters to improve the server's ability to accommodate semi-connected and alleviate the queue overflow problem caused by SYN flood attacks. However, this method can only temporarily alleviate and cannot fundamentally solve the attack.

2, block malicious sources Internet Protocol Address

use firewall or iptables rules to ban the source IP of the attack traffic. If the attack IP is more concentrated, it can be directly banned in batches; if the IP is scattered, the effective request volume of SYN flood attack can be reduced by analyzing the traffic characteristics, banning abnormal network segments or setting IP access frequency limits. It is necessary to pay attention to avoid mistakenly blocking normal user IP, and the banning rules can be dynamically adjusted in combination with traffic logs.

3. Advanced protection strategies for SYN flood attacks

basic disposal can only temporarily stop loss. To build a more stable defense system, it is necessary to adopt advanced protection strategies to reduce the impact of SYN flood attacks from the root.

1. Enable SYN Cookies authentication mechanism

SYN Cookies is a protection technology against SYN flood attacks. When the server's half-connection queue is full, it will generate SYN cookie values instead of half-connection queue storage through encryption algorithms, and only establish connections when normal ACK packets are received. After enabling this mechanism, the server does not need to reserve half-connection resources for malicious SYN requests, which can effectively resist the occupation of resources by SYN flood attacks.

2, deployment load balancing and flow cleaning

traffic delivery to multiple servers through load balancing equipment to disperse the pressure of SYN flood attacks and avoid centralized attacks on single servers. At the same time, it can be matched with professional traffic cleaning equipment to detect the traffic entering the network, filter out the attack traffic containing malicious SYN packets, and only forward normal traffic to the back-end server to block SYN flood attacks from the entrance.

4. How to prevent the recurrence of SYN flood attacks?

emergency response is an afterthought, daily prevention is the core to reduce the risk of SYN flood attacks, and defense barriers need to be built from multiple dimensions such as network architecture and system configuration.

1, optimize network architecture and configuration

adopts multi-layer network architecture, deploys firewalls, intrusion detection systems and other security devices in the front end of the server, and sets strict access control rules. Regularly update the system kernel and security patches, close unnecessary ports and services, and reduce the potential entry of SYN flood attacks. At the same time, reasonably adjust TCP connection parameters, such as shortening SYN timeout time and reducing the occupation time of semi-connected resources.

2, establish a regular monitoring and early warning mechanism

build a monitoring platform for network traffic and server status, set the warning threshold of SYN connection number, bandwidth usage and other indicators, and trigger the alarm in time when the indicator is abnormal. Regularly carry out security drills to simulate SYN flood attack scenarios, test the effectiveness of emergency response processes, and improve the response speed and coping ability of operation and maintenance personnel.

To sum up, the response to SYN flood attacks needs to follow the whole process logic of identification, disposal, protection and prevention. Start with quickly identifying attack characteristics, temporarily stop losses through basic emergency means, and then use advanced protection strategies to strengthen defense capabilities, and finally reduce attack risks through normalized preventive measures. Only by building a complete system from temporary disposal to long-term defense can we effectively resist SYN flood attacks and ensure the continuous and stable operation of network services.