Limit Single-IP Concurrent Connections in CC Attacks

Limiting concurrent connections per IP is essential for defending your Hong Kong server against a malicious CC attack. By setting safe limits to limit concurrent connections, you can block suspicious activity without impacting normal users. Most browsers typically open no more than six connections at once. The following table outlines the recommended values for connection limits:

Monitoring these limits helps ensure your website remains stable and responsive.

Key Takeaways

• Limit concurrent connections per IP to protect your server from CC attacks. Set limits above normal browser usage to block attackers while allowing real users access.
• Monitor traffic patterns regularly. Look for spikes in connections from single IP addresses to identify potential attacks early.
• Use server configurations like Nginx or Apache to enforce connection limits. Implement modules that help track and block excessive requests from malicious users.
• Adjust connection limits based on user groups. Trusted users may need higher limits than public visitors to ensure smooth access.
• Log denied connection attempts to analyze attack patterns. Use this data to fine-tune your security settings and improve defenses.

Understanding CC Attacks

What Is a CC Attack?

A CC attack, or Challenge Collapsar attack, targets your server by sending a large number of HTTP requests in a short time. Attackers use automated tools or botnets to flood your website with traffic. This flood can slow down your site or even make it crash. You may notice your server becomes unresponsive or your website loads very slowly. Attackers often use many different IP addresses, but sometimes they focus on sending many requests from a single IP.

You need to recognize the signs of a CC attack early. Watch for sudden spikes in traffic or a high number of connections from one IP address. These attacks can harm your website’s reputation and cause real losses for your business.

Why Limit Concurrent Connections Works

When you limit concurrent connections from each IP, you control how many requests a single user can make at the same time. This method helps you stop attackers from overwhelming your server with too many connections. Most real users, like those using a web browser, only open a few connections at once. Attackers, on the other hand, try to open dozens or even hundreds.

Tip: Setting your connection limit just above normal browser usage (for example, more than 6 connections) helps you block attackers while letting real users browse without problems.

The following table explains why this strategy works:

By using the limit concurrent connections approach, you protect your server from overload. You also make sure your real visitors can always reach your website.

Limit Concurrent Connections: Server Setup

Nginx Per-IP Limits

You can use Nginx to limit concurrent connections from each IP address. This helps you stop attackers from opening too many connections at once. Nginx uses two main directives for this:

• limit_conn_zone: This sets up a shared memory zone to track connections per IP.
• limit_conn: This applies the actual connection limit in your server or location block.

Here is how you can set it up:

http {
    limit_conn_zone $binary_remote_addr zone=addr:10m;

    server {
        location / {
            limit_conn addr 10;
        }
    }
}

This example allows up to 10 concurrent connections per IP. You should set this number above normal browser usage. Most browsers use 6 connections, so 10 gives real users enough room. If you notice attackers still getting through, you can lower the limit.

Tip: Monitor your logs after setting these limits. Adjust the value if you see too many legitimate users getting blocked.

Apache Per-IP Limits

Apache gives you several ways to limit concurrent connections. You can use modules like mod_evasive and mod_reqtimeout to help protect your server.

You can add these modules and set limits in your configuration file. For example, with mod_evasive:

<IfModule mod_evasive20.c>
    DOSHashTableSize    3097
    DOSPageCount        5
    DOSSiteCount        20
    DOSBlockingPeriod   10
</IfModule>

This setup blocks IPs that make too many requests in a short time. You can also use mod_reqtimeout to limit how long a connection can stay open. Both modules help you limit concurrent connections and reduce the risk of CC attacks.

• mod_reqtimeout restricts the minimum transfer speed for connections.
• mod_evasive limits the number of connections from a single IP.
• Both modules help stop attacks like Slowloris.

Note: Always set your limits above normal user activity. Start with 10-20 connections per IP and adjust as needed.

Squid Proxy Limits

If you use Squid as a proxy, you can control the maximum concurrent connections per client IP. Squid uses access control lists (ACLs) and special parameters for this.

Here is a sample configuration:

acl maxcon_clients maxconn 10
http_access deny maxcon_clients

This setup denies access to any client IP with more than 10 concurrent connections. Make sure you enable client_db for this to work. You should also create access control policies for trusted hosts and set operational hours if needed. These steps help you prevent service disruption during a CC attack.

• Allow or restrict access based on trusted IPs or domains.
• Set proxy usage hours to limit risk during peak attack times.

Hosting Panel Settings

Many hosting panels let you set connection limits through their security settings. You can usually find these options in the control panel under security or network settings.

Set your connection hard limit above normal browser usage. Most users need 4 to 10 connections. This range helps you block attackers but keeps your site friendly for real visitors. Some panels also offer a “Network Quota” or similar feature. Use this to further control resource usage and protect your server.

Tip: Review your panel’s documentation for exact steps. Each hosting provider may use different terms or settings.

By using these server setup options, you can limit concurrent connections and protect your site from CC attacks. Always monitor your traffic and adjust your settings as needed to keep your site safe and responsive.

Set and Adjust Connection Limits

Enable Required Features

You need to activate the right modules and settings before you can limit concurrent connections. Each server environment has its own requirements. Follow these steps to prepare your system:

1. Set the MaxConnections parameter in your web server plug-in configuration. This controls how many connections each child process can handle.
2. Reduce the TCP listen backlog in your application server. This helps manage incoming workload and prevents overload.
3. Monitor MaxConnections usage. Set LogLevel to “Stats” and use piped logging to filter connection events.
4. Check and configure the kernel file-max by editing /etc/sysctl.conf. Increase the maximum number of open files if your server needs to handle more connections.
5. Adjust the process file-max (ulimit) for your web server user in /etc/security/limits.conf.
6. Modify the systemd unit file for Nginx. Set LimitNOFILE to allow the desired number of connections.
7. Verify the kernel’s current file-max limit using cat /proc/sys/fs/file-max.
8. Apply changes with sysctl -p after editing /etc/sysctl.conf.

Tip: Always confirm your changes with commands like sysctl net.ipv4.tcp_max_syn_backlog and check the ulimit for your web server user. This ensures your server can support the connection limits you set.

Apply Per-IP Limits

Once you enable the required features, you can apply per-IP connection limits. This step helps you control how many simultaneous connections each IP address can make. Use these steps to set up per-IP limits on Linux-based servers:

1. Check the current connection limits with sysctl net.ipv4.tcp_max_syn_backlog.
2. Increase the TCP connection limit by editing net.ipv4.tcp_max_syn_backlog in /etc/sysctl.conf.
3. Set soft and hard limits for open files in /etc/security/limits.conf.
4. Update the system-wide file descriptor limit by changing fs.file-max in /etc/sysctl.conf.
5. Verify your new settings with sysctl net.ipv4.tcp_max_syn_backlog.

You should monitor traffic patterns after you set these limits. Look for spikes in connections from single IP addresses. Adjust your limits if you see legitimate users getting blocked or attackers bypassing your settings. Most browsers use up to six connections, so setting your limit above this number helps you avoid blocking real users.

Note: Use logs and monitoring tools to track active connections. This helps you fine-tune your settings and respond quickly to unusual activity.

Block Malicious IPs

Blocking malicious IPs is a key part of defending your server during a CC attack. You need to identify suspicious activity and act fast. Use criteria like request rate and source IP to spot attackers. The table below shows how you can use rate limit mode to block harmful traffic:

You should block IPs that exceed your connection or request limits. However, you must watch for false positives. Blocking legitimate users can cause alert fatigue, waste resources, and frustrate your security team. Always review logs and unblock users if you see mistakes.

Alert: False positives can lead to wasted resources and frustration. Monitor your blocks and adjust your criteria to avoid unnecessary disruptions.

Adjust Limits for User Groups

Different user groups may need different connection limits. For example, trusted partners or internal users often require higher limits than public visitors. You can create access control lists or user profiles to set custom limits.

• Assign higher connection limits to trusted IPs or domains.
• Set lower limits for anonymous or public users.
• Monitor usage and adjust limits based on real-world traffic patterns.

You should review your settings regularly. Look for changes in user behavior or new attack patterns. Adjust your limits to keep your site secure and user-friendly.

Tip: Always balance security and usability. Limit concurrent connections to block attackers, but give real users enough room to browse and interact with your site.

By following these steps, you can set and adjust connection limits effectively. You protect your server from CC attacks and keep your website responsive for everyone.

Monitor and Fine-Tune

Monitor Active Connections

You need to keep an eye on active connections to spot unusual spikes or patterns. Real-time monitoring helps you react quickly to threats and adjust your limits as needed. Several tools can help you track active connections per IP:

• Nagios Network Analyzer: Gives you real-time updates and packet analysis. You can see traffic flows and capture packets for deeper inspection.
• Zabbix Network Monitoring: Collects network metrics and supports SNMP. It also alerts you when it detects anomalies.
• SolarWinds Network Performance Monitor: Offers end-to-end visibility and automatic device discovery. It sends intelligent alerts based on performance trends.
• PRTG Network Monitor: Monitors devices, bandwidth, and applications. You can set up customizable alerts for different connection thresholds.

Tip: Use these tools to set up alerts for sudden increases in connections from a single IP. This helps you catch attacks early.

Log Denied Attempts

You should always log denied connection attempts. These logs help you understand attack patterns and identify which IPs try to exceed your limits. Review your logs regularly to spot trends or repeated offenders. Many monitoring tools let you filter logs by IP address or time period. This makes it easier to find suspicious activity.

• Store logs securely so attackers cannot tamper with them.
• Set up automated alerts for repeated denied attempts from the same IP.
• Use log data to update your firewall or blocklists.

Note: Reviewing logs helps you fine-tune your settings and improve your defenses over time.

Choose Safe Limit Values

Choosing the right connection limit values depends on your server type. Static content servers, like those serving images or HTML files, usually need lower connection limits. They deliver files quickly and do not use many resources per connection. Dynamic application servers, such as Payara, handle more complex tasks and database operations. These servers can support higher connection limits because they manage more resources.

• Static content servers often use lower limits to prevent overload.
• Dynamic application servers can handle more connections due to their design.
• Adjust settings like MaxConnections and ThreadsPerChild to match your server’s workload.

Alert: Always test your limits during normal traffic. Raise or lower them based on real user activity and server performance.

You protect your website from CC attacks when you limit concurrent connections per IP. This step keeps your server stable and helps real users access your site. Regular monitoring lets you spot new threats and adjust your settings for better security. Review your security settings often. Stay proactive to keep your website safe and responsive.

FAQ

How do I know if my server is under a CC attack?

You may notice your website loads slowly or stops responding. Check your server logs for many requests from the same IP. Use monitoring tools to spot sudden spikes in traffic.

What is a safe limit for concurrent connections per IP?

Set your limit above normal browser use. Most browsers open up to 6 connections. A safe starting point is 10 connections per IP. Adjust this number based on your website’s traffic.

Will limiting connections block real users?

If you set your limits too low, some real users may get blocked. Always monitor your logs and adjust the limits. Start with a higher value and lower it only if you see attacks.

Can I use a firewall to help limit connections?

Yes! Firewalls can block IPs that exceed your set limits. You can use tools like iptables or cloud-based firewalls. Combine these with server settings for stronger protection.