When optimizing and improving firewall policies and performance on US VPSs, operations and maintenance personnel must focus on ensuring security while minimizing the negative impact of firewall policies on network performance. Mainstream Linux distributions like CentOS and Ubuntu often come pre-installed with iptables or firewalld, while Windows Server has built-in advanced firewall features. Therefore, optimization should be tailored to the operating system type and business needs.

In Linux systems, iptables and nftables are common firewall tools. The more complex the iptables rules, the greater the overhead of processing each packet. Therefore, the primary goal of optimizing policies is to reduce redundant rules and duplicate checks. First, run the following command to review existing rules:

iptables -L -n -v

Rules that have been unused for a long time should be cleaned up promptly to ensure a concise rule set. If the system has been upgraded to support nftables, consider migrating, as nftables offers better performance and scalability, making it suitable for large-scale rule management. To perform this migration, use:

nft list ruleset

to review existing rules and convert iptables rules to nftables format using a script.

Firewalld, the default firewall front-end for CentOS, features dynamic updates to avoid disrupting existing connections when applying rules. For multi-application deployments, such as those common in US VPS environments, it's recommended to adopt a zoned approach. This approach divides different services into zones, reduces reliance on global rules, and improves matching efficiency. You can view and adjust zones using the following commands:

firewall-cmd --get-active-zones
firewall-cmd --zone=public --add-service=http --permanent
firewall-cmd --reload

While balancing security and performance, firewalls should adhere to the principle of minimal openness, allowing only essential ports and avoiding wide-ranging port blocks. For high-risk services such as database port 3306 or remote desktop port 3389, configure source IP restrictions. For example:

firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="203.0.113.10" port protocol="tcp" port="3306" accept'

firewall-cmd --reload

This approach improves security while reducing unnecessary matching logic and CPU usage.

For performance optimization, rule order is also important. iptables or firewalld processes packets sequentially from top to bottom, so frequently used rules should be placed at the front to avoid redundant checks on all packets. For example, if the SSH service only allows access from specific source IP addresses, this rule should be placed early, rather than after all default deny rules. You can ensure that high-priority rules are at the top of the rule set by running:

iptables -I INPUT 1 -p tcp --dport 22 -s 203.0.113.10 -j ACCEPT

This ensures that high-priority rules are placed at the top of the rule set.

In high-concurrency scenarios, US VPSs may experience a large number of connection requests, and the firewall's state tracking mechanism may become a performance bottleneck. The conntrack module in the Linux kernel tracks connection state. While this improves security, it also increases resource consumption under high traffic. This can be optimized by adjusting the kernel parameter:

sysctl -w net.netfilter.nf_conntrack_max=262144

This parameter defines the maximum number of tracked connections. Increasing it appropriately can prevent packet drops caused by connection overflow. Alternatively, you can disable state tracking for services with lower security requirements to improve throughput.

For DDoS attack protection, rate limiting policies should be implemented in the firewall. iptables supports limiting the connection rate using the limit module. For example:

iptables -A INPUT -p tcp --dport 80 -m limit --limit 50/s --limit-burst 200 -j ACCEPT

This rule limits port 80 to a maximum of 50 connection requests per second and allows a burst of 200 requests. This type of policy can reduce the impact of malicious traffic and improve overall stability under high-concurrency conditions.

With the increasing popularity of IPv6, most US VPS providers support IPv6 addresses, and firewall policies must be optimized accordingly. If the system is not configured with IPv6 rules, it may default to a fully open state, which poses serious risks. Instead, use:

ip6tables -L -n -v

Check IPv6 rules to ensure consistency with IPv4 policies to avoid inadvertent security vulnerabilities.

In Windows Server environments, firewall optimization focuses on rule grouping and log auditing. Using Windows Firewall with Advanced Security, you can define independent rules for different applications and deploy them in batches using Group Policy, improving management efficiency. Regarding performance, avoid creating too many fine-grained rules. Instead, combine network-layer filtering with application-layer rules to reduce processing overhead.

In addition to the system's internal firewall, US VPSs often operate under the protection of the provider's security group policies. When optimizing, it's important to coordinate the VPS's firewall with the cloud provider's protection policies to avoid double filtering and rule conflicts. For example, if the cloud service's security group restricts access to specific port sources, the VPS's internal firewall can simplify the corresponding rules, reducing system-level processing overhead.

Firewall policy optimization should also be combined with log analysis to promptly identify potential abnormal traffic and attack behavior. In Linux, you can enable iptables logging:

iptables -A INPUT -p tcp --dport 22 -j LOG --log-prefix "SSH attempt: "

Use system log analysis tools to identify high-frequency attack IP addresses and integrate with fail2ban to automatically block them. This type of automated protection not only improves security but also reduces the burden of manual maintenance on administrators.

Overall, the core approach to optimizing US VPS firewalls lies in streamlining rules, optimizing sequencing, controlling state tracking, judiciously utilizing rate limits, and integrating log analysis. These measures significantly reduce system resource consumption and improve network throughput while ensuring security. Combined with the VPS operator's external security group policy for unified management, this approach achieves a balance between security and performance in cross-border business, content distribution, and high-concurrency application scenarios, ensuring continuous and stable business operations.