Performance-Related Firewall Issues

Performance-Related Firewall Issues

Firewall processing can impact website performance, particularly during high traffic periods or when rules aren't optimized. Identifying and resolving performance bottlenecks maintains both security and user experience.

High Latency from Rule Processing: Complex rule sets with inefficient ordering cause noticeable delays:

# Firewall performance analyzer
import time
import subprocess
import statistics

class FirewallPerformanceAnalyzer:
    def __init__(self):
        self.results = {}
        
    def measure_rule_performance(self):
        """Measure processing time for firewall rules"""
        
        # Get current rules with packet counters
        rules_output = subprocess.check_output(
            ["iptables", "-L", "-v", "-n", "--line-numbers"],
            text=True
        )
        
        # Parse rules and their hit counts
        rules = []
        for line in rules_output.split('\n'):
            if 'pkts' not in line and any(x in line for x in ['ACCEPT', 'DROP', 'REJECT']):
                parts = line.split()
                if len(parts) > 2:
                    rules.append({
                        'num': parts[0] if parts[0].isdigit() else 0,
                        'pkts': int(parts[1]) if parts[1].isdigit() else 0,
                        'rule': ' '.join(parts[2:])
                    })
        
        # Analyze rule efficiency
        total_packets = sum(r['pkts'] for r in rules)
        if total_packets > 0:
            for rule in rules:
                rule['percentage'] = (rule['pkts'] / total_packets) * 100
        
        # Sort by packet count to identify optimization opportunities
        rules.sort(key=lambda x: x['pkts'], reverse=True)
        
        print("=== Firewall Rule Performance Analysis ===")
        print(f"Total packets processed: {total_packets}")
        print("\nTop 10 most-hit rules (candidates for reordering):")
        
        for i, rule in enumerate(rules[:10]):
            print(f"{i+1}. Rule #{rule['num']}: {rule['pkts']} packets ({rule['percentage']:.1f}%)")
            print(f"   {rule['rule'][:80]}...")
        
        return rules
    
    def benchmark_connection_time(self, target_url, iterations=100):
        """Measure connection establishment time"""
        
        times = []
        
        for i in range(iterations):
            start = time.time()
            try:
                result = subprocess.run(
                    ["curl", "-o", "/dev/null", "-s", "-w", "%{time_connect}", target_url],
                    capture_output=True,
                    text=True,
                    timeout=5
                )
                connection_time = float(result.stdout)
                times.append(connection_time)
            except:
                continue
            
            # Small delay between tests
            time.sleep(0.1)
        
        if times:
            print(f"\n=== Connection Time Analysis ({iterations} samples) ===")
            print(f"Average: {statistics.mean(times)*1000:.2f}ms")
            print(f"Median: {statistics.median(times)*1000:.2f}ms")
            print(f"Min: {min(times)*1000:.2f}ms")
            print(f"Max: {max(times)*1000:.2f}ms")
            print(f"StdDev: {statistics.stdev(times)*1000:.2f}ms")
            
            # Identify outliers
            avg = statistics.mean(times)
            outliers = [t for t in times if t > avg * 2]
            if outliers:
                print(f"Outliers detected: {len(outliers)} connections took >2x average time")
        
        return times

Connection Table Exhaustion: High-traffic websites can exhaust firewall connection tracking tables:

# Monitor connection tracking
# Check current usage
cat /proc/sys/net/netfilter/nf_conntrack_count
cat /proc/sys/net/netfilter/nf_conntrack_max

# Monitor in real-time
watch -n 1 'echo "Connections: $(cat /proc/sys/net/netfilter/nf_conntrack_count) / $(cat /proc/sys/net/netfilter/nf_conntrack_max)"'

# Increase limits if needed
echo 262144 > /proc/sys/net/netfilter/nf_conntrack_max

# Make permanent
echo "net.netfilter.nf_conntrack_max = 262144" >> /etc/sysctl.conf
sysctl -p

# Tune connection timeouts
sysctl -w net.netfilter.nf_conntrack_tcp_timeout_established=300
sysctl -w net.netfilter.nf_conntrack_tcp_timeout_time_wait=30
sysctl -w net.netfilter.nf_conntrack_tcp_timeout_close_wait=30