21 Dec 2025 Internet Networking

Test HTTP/2 Max Concurrent Streams: Tools & Guide

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Testing HTTP/2 max concurrent streams requires tools such as h2load, curl with HTTP/2 support, or custom scripts using the h2 Python library. Run h2load with flags like -n 100 -c 1 -m 200 to observe where your server enforces limits. Proper enforcement of SETTINGS_MAX_CONCURRENT_STREAMS defends against CVE-2023-44487 Rapid Reset attacks and ensures stable performance under load.

CloudScale AI SEO - Article Summary

1.
What it is
This article explains how to test HTTP/2 server configurations to verify they properly enforce maximum concurrent stream limits using a Python script and monitoring tools.
2.
Why it matters
Servers that don't enforce stream limits are vulnerable to HTTP/2 attacks and resource exhaustion, making this testing critical for security hardening and performance optimization.
3.
Key takeaway
Use the provided Python script to verify your server actually enforces its advertised HTTP/2 stream limits and configure conservative limits of 100-128 streams for security.

~6 min read

1. Introduction

Understanding and testing your server’s maximum concurrent stream configuration is critical for both performance tuning and security hardening against HTTP/2 attacks. This guide provides comprehensive tools and techniques to test the SETTINGS_MAX_CONCURRENT_STREAMS parameter on your web servers.

This article complements our previous guide on Testing Your Website for HTTP/2 Rapid Reset Vulnerabilities from a macOS. While that article focuses on the CVE-2023-44487 Rapid Reset attack, this guide helps you verify that your server properly enforces stream limits, which is a critical defense mechanism.

2. Why Test Stream Limits?

The SETTINGS_MAX_CONCURRENT_STREAMS setting determines how many concurrent requests a client can multiplex over a single HTTP/2 connection. Testing this limit is important because:

Security validation: Confirms your server enforces reasonable stream limits
Configuration verification: Ensures your settings match security recommendations (typically 100-128 streams)
Performance tuning: Helps optimize the balance between throughput and resource consumption
Attack surface assessment: Identifies if servers accept dangerously high stream counts

3. Understanding HTTP/2 Stream Limits

When an HTTP/2 connection is established, the server sends a SETTINGS frame that includes:

SETTINGS_MAX_CONCURRENT_STREAMS: 100

This tells the client the maximum number of concurrent streams allowed. A compliant client should respect this limit, but attackers will not.

3.1. Common Default Values

Web Servers:

Nginx: 128 (configurable via http2_max_concurrent_streams)
Apache: 100 (configurable via H2MaxSessionStreams)
Caddy: 250 (configurable via max_concurrent_streams)
LiteSpeed: 100 (configurable in admin panel)

Reverse Proxies and Load Balancers:

HAProxy: No default limit (should be explicitly configured)
Envoy: 100 (configurable via max_concurrent_streams)
Traefik: 250 (configurable via maxConcurrentStreams)

CDN and Cloud Services:

CloudFlare: 128 (managed automatically)
AWS ALB: 128 (managed automatically)
Azure Front Door: 100 (managed automatically)

4. The Stream Limit Testing Script

The following Python script tests your server’s maximum concurrent streams using the h2 library. This script will:

Connect to your HTTP/2 server
Read the advertised SETTINGS_MAX_CONCURRENT_STREAMS value
Attempt to open more streams than the advertised limit
Verify that the server actually enforces the limit
Provide detailed results and recommendations

4.1. Prerequisites

Install the required Python libraries:

pip3 install h2 hyper --break-system-packages

Verify installation:

python3 -c "import h2; print(f'h2 version: {h2.__version__}')"

4.2. Complete Script

Save the following as http2_stream_limit_tester.py:

#!/usr/bin/env python3
"""
HTTP/2 Maximum Concurrent Streams Tester

Tests the SETTINGS_MAX_CONCURRENT_STREAMS limit on HTTP/2 servers
and attempts to exceed it to verify enforcement.

Usage:
    python3 http2_stream_limit_tester.py --host example.com --port 443

Requirements:
    pip3 install h2 hyper --break-system-packages
"""

import argparse
import socket
import ssl
import time
from typing import Dict, List, Optional, Tuple
from dataclasses import dataclass, field

try:
    from h2.connection import H2Connection
    from h2.config import H2Configuration
    from h2.events import (
        RemoteSettingsChanged,
        StreamEnded,
        DataReceived,
        StreamReset,
        WindowUpdated,
        SettingsAcknowledged,
        ResponseReceived
    )
    from h2.exceptions import ProtocolError
except ImportError:
    print("Error: h2 library not installed")
    print("Install with: pip3 install h2 hyper --break-system-packages")
    exit(1)


@dataclass
class StreamLimitTestResults:
    """Results from stream limit testing"""
    advertised_max_streams: Optional[int] = None
    actual_max_streams: int = 0
    successful_streams: int = 0
    failed_streams: int = 0
    reset_streams: int = 0
    enforcement_detected: bool = False
    test_duration: float = 0.0
    server_settings: Dict = field(default_factory=dict)
    errors: List[str] = field(default_factory=list)


class HTTP2StreamLimitTester:
    """Test HTTP/2 server stream limits"""

    def __init__(
        self,
        host: str,
        port: int = 443,
        path: str = "/",
        use_tls: bool = True,
        timeout: int = 30,
        verbose: bool = False
    ):
        self.host = host
        self.port = port
        self.path = path
        self.use_tls = use_tls
        self.timeout = timeout
        self.verbose = verbose

        self.socket: Optional[socket.socket] = None
        self.h2_conn: Optional[H2Connection] = None
        self.server_max_streams: Optional[int] = None
        self.active_streams: Dict[int, dict] = {}

    def connect(self) -> bool:
        """Establish connection to the server"""
        try:
            # Create socket
            self.socket = socket.create_connection(
                (self.host, self.port),
                timeout=self.timeout
            )

            # Wrap with TLS if needed
            if self.use_tls:
                context = ssl.create_default_context()
                context.check_hostname = True
                context.verify_mode = ssl.CERT_REQUIRED

                # Set ALPN protocols for HTTP/2
                context.set_alpn_protocols(['h2', 'http/1.1'])

                self.socket = context.wrap_socket(
                    self.socket,
                    server_hostname=self.host
                )

                # Verify HTTP/2 was negotiated
                negotiated_protocol = self.socket.selected_alpn_protocol()
                if negotiated_protocol != 'h2':
                    raise Exception(f"HTTP/2 not negotiated. Got: {negotiated_protocol}")

                if self.verbose:
                    print(f"TLS connection established (ALPN: {negotiated_protocol})")

            # Initialize HTTP/2 connection
            config = H2Configuration(client_side=True)
            self.h2_conn = H2Connection(config=config)
            self.h2_conn.initiate_connection()

            # Send connection preface
            self.socket.sendall(self.h2_conn.data_to_send())

            # Receive server settings
            self._receive_data()

            if self.verbose:
                print(f"HTTP/2 connection established to {self.host}:{self.port}")

            return True

        except Exception as e:
            if self.verbose:
                print(f"Connection failed: {e}")
            return False

    def _receive_data(self, timeout: Optional[float] = None) -> List:
        """Receive and process data from server"""
        if timeout:
            self.socket.settimeout(timeout)
        else:
            self.socket.settimeout(self.timeout)

        events = []
        try:
            data = self.socket.recv(65536)
            if not data:
                return events

            events_received = self.h2_conn.receive_data(data)

            for event in events_received:
                events.append(event)

                if isinstance(event, RemoteSettingsChanged):
                    self._handle_settings(event)
                elif isinstance(event, ResponseReceived):
                    if self.verbose:
                        print(f"  Stream {event.stream_id}: Response received")
                elif isinstance(event, DataReceived):
                    if self.verbose:
                        print(f"  Stream {event.stream_id}: Data received ({len(event.data)} bytes)")
                elif isinstance(event, StreamEnded):
                    if self.verbose:
                        print(f"  Stream {event.stream_id}: Ended normally")
                    if event.stream_id in self.active_streams:
                        self.active_streams[event.stream_id]['ended'] = True
                elif isinstance(event, StreamReset):
                    if self.verbose:
                        print(f"  Stream {event.stream_id}: Reset (error code: {event.error_code})")
                    if event.stream_id in self.active_streams:
                        self.active_streams[event.stream_id]['reset'] = True

            # Send any pending data
            data_to_send = self.h2_conn.data_to_send()
            if data_to_send:
                self.socket.sendall(data_to_send)

        except socket.timeout:
            pass
        except Exception as e:
            if self.verbose:
                print(f"Error receiving data: {e}")

        return events

    def _handle_settings(self, event: RemoteSettingsChanged):
        """Handle server settings"""
        for setting, value in event.changed_settings.items():
            setting_name = setting.name if hasattr(setting, 'name') else str(setting)

            if self.verbose:
                print(f"  Server setting: {setting_name} = {value}")

            # Check for MAX_CONCURRENT_STREAMS
            if 'MAX_CONCURRENT_STREAMS' in setting_name:
                self.server_max_streams = value
                if self.verbose:
                    print(f"Server advertises max concurrent streams: {value}")

    def send_stream_request(self, stream_id: int) -> bool:
        """Send a GET request on a specific stream"""
        try:
            headers = [
                (':method', 'GET'),
                (':path', self.path),
                (':scheme', 'https' if self.use_tls else 'http'),
                (':authority', self.host),
                ('user-agent', 'HTTP2-Stream-Limit-Tester/1.0'),
            ]

            self.h2_conn.send_headers(stream_id, headers, end_stream=True)
            data_to_send = self.h2_conn.data_to_send()

            if data_to_send:
                self.socket.sendall(data_to_send)

            self.active_streams[stream_id] = {
                'sent': time.time(),
                'ended': False,
                'reset': False
            }

            return True

        except ProtocolError as e:
            if self.verbose:
                print(f"  Stream {stream_id}: Protocol error - {e}")
            return False
        except Exception as e:
            if self.verbose:
                print(f"  Stream {stream_id}: Failed to send - {e}")
            return False

    def test_concurrent_streams(
        self,
        max_streams_to_test: int = 200,
        batch_size: int = 10,
        delay_between_batches: float = 0.1
    ) -> StreamLimitTestResults:
        """
        Test maximum concurrent streams by opening multiple streams

        Args:
            max_streams_to_test: Maximum number of streams to attempt
            batch_size: Number of streams to open per batch
            delay_between_batches: Delay in seconds between batches
        """
        results = StreamLimitTestResults()
        start_time = time.time()

        print(f"\nTesting HTTP/2 Stream Limits:")
        print(f"  Target: {self.host}:{self.port}")
        print(f"  Max streams to test: {max_streams_to_test}")
        print(f"  Batch size: {batch_size}")
        print("=" * 60)

        try:
            # Connect and get initial settings
            if not self.connect():
                results.errors.append("Failed to establish connection")
                return results

            results.advertised_max_streams = self.server_max_streams

            if self.server_max_streams:
                print(f"\nServer advertised limit: {self.server_max_streams} concurrent streams")
            else:
                print(f"\nServer did not advertise MAX_CONCURRENT_STREAMS limit")

            # Start opening streams in batches
            stream_id = 1  # HTTP/2 client streams use odd numbers
            streams_opened = 0

            while streams_opened  results.reset_streams:
                    new_resets = reset_count - results.reset_streams
                    results.reset_streams = reset_count
                    print(f"  WARNING: {new_resets} stream(s) were reset by server")

                    # If we're getting lots of resets, enforcement is happening
                    if reset_count > (results.successful_streams * 0.1):
                        results.enforcement_detected = True
                        print(f"  Stream limit enforcement detected")

                # Small delay between batches
                if delay_between_batches > 0 and streams_opened  128:
            print(f"\nWARNING: Advertised limit ({results.advertised_max_streams}) exceeds recommended maximum (128)")
            print("  Consider reducing http2_max_concurrent_streams")
        elif results.advertised_max_streams and results.advertised_max_streams  150:
            print(f"\nWARNING: Opened {results.actual_max_streams} streams without enforcement")
            print("  Server may be vulnerable to stream exhaustion attacks")
        elif results.enforcement_detected:
            print(f"\nServer actively enforces stream limits")
            print("  Stream limit protection is working correctly")

        if results.errors:
            print(f"\nErrors encountered:")
            for error in results.errors:
                print(f"  {error}")

        print("=" * 60 + "\n")

    def close(self):
        """Close the connection"""
        try:
            if self.h2_conn:
                self.h2_conn.close_connection()
                if self.socket:
                    data_to_send = self.h2_conn.data_to_send()
                    if data_to_send:
                        self.socket.sendall(data_to_send)

            if self.socket:
                self.socket.close()

            if self.verbose:
                print("Connection closed")
        except Exception as e:
            if self.verbose:
                print(f"Error closing connection: {e}")


def main():
    parser = argparse.ArgumentParser(
        description='Test HTTP/2 server maximum concurrent streams',
        formatter_class=argparse.RawDescriptionHelpFormatter,
        epilog="""
Examples:
  # Basic test
  python3 http2_stream_limit_tester.py --host example.com

  # Test with custom parameters
  python3 http2_stream_limit_tester.py --host example.com --max-streams 300 --batch 20

  # Verbose output
  python3 http2_stream_limit_tester.py --host example.com --verbose

  # Test specific path
  python3 http2_stream_limit_tester.py --host example.com --path /api/health

  # Test non-TLS HTTP/2 (h2c)
  python3 http2_stream_limit_tester.py --host localhost --port 8080 --no-tls

Prerequisites:
  pip3 install h2 hyper --break-system-packages
        """
    )

    parser.add_argument('--host', required=True, help='Target hostname')
    parser.add_argument('--port', type=int, default=443, help='Target port (default: 443)')
    parser.add_argument('--path', default='/', help='Request path (default: /)')
    parser.add_argument('--no-tls', action='store_true', help='Disable TLS (for h2c testing)')
    parser.add_argument('--max-streams', type=int, default=200,
                       help='Maximum streams to test (default: 200)')
    parser.add_argument('--batch', type=int, default=10,
                       help='Streams per batch (default: 10)')
    parser.add_argument('--delay', type=float, default=0.1,
                       help='Delay between batches in seconds (default: 0.1)')
    parser.add_argument('--timeout', type=int, default=30,
                       help='Connection timeout in seconds (default: 30)')
    parser.add_argument('--verbose', action='store_true', help='Enable verbose output')

    args = parser.parse_args()

    print("=" * 60)
    print("HTTP/2 Maximum Concurrent Streams Tester")
    print("=" * 60)

    tester = HTTP2StreamLimitTester(
        host=args.host,
        port=args.port,
        path=args.path,
        use_tls=not args.no_tls,
        timeout=args.timeout,
        verbose=args.verbose
    )

    try:
        results = tester.test_concurrent_streams(
            max_streams_to_test=args.max_streams,
            batch_size=args.batch,
            delay_between_batches=args.delay
        )

        tester.display_results(results)

    except KeyboardInterrupt:
        print("\n\nTest interrupted by user")
    except Exception as e:
        print(f"\nFatal error: {e}")
        if args.verbose:
            import traceback
            traceback.print_exc()


if __name__ == '__main__':
    main()

5. Using the Script

5.1. Basic Usage

Test your server with default settings:

python3 http2_stream_limit_tester.py --host example.com

5.2. Advanced Examples

Test with increased stream count:

python3 http2_stream_limit_tester.py --host example.com --max-streams 300 --batch 20

Verbose output for debugging:

python3 http2_stream_limit_tester.py --host example.com --verbose

Test specific API endpoint:

python3 http2_stream_limit_tester.py --host api.example.com --path /v1/health

Test non-TLS HTTP/2 (h2c):

python3 http2_stream_limit_tester.py --host localhost --port 8080 --no-tls

Gradual escalation test:

# Start conservative
python3 http2_stream_limit_tester.py --host example.com --max-streams 50

# Increase if server handles well
python3 http2_stream_limit_tester.py --host example.com --max-streams 100

# Push to limits
python3 http2_stream_limit_tester.py --host example.com --max-streams 200

Fast burst test:

python3 http2_stream_limit_tester.py --host example.com --max-streams 150 --batch 30 --delay 0.01

Slow ramp test:

python3 http2_stream_limit_tester.py --host example.com --max-streams 200 --batch 5 --delay 0.5

6. Understanding the Results

The script provides detailed output including:

Advertised max streams: What the server claims to support
Successful stream opens: How many streams were successfully created
Failed stream opens: Streams that failed to open
Streams reset by server: Streams terminated by the server (enforcement)
Actual max achieved: The real concurrent stream limit

6.1. Example Output

Testing HTTP/2 Stream Limits:
  Target: example.com:443
  Max streams to test: 200
  Batch size: 10
============================================================

Server advertised limit: 128 concurrent streams

Opening batch of 10 streams (total: 10)...
Opening batch of 10 streams (total: 20)...
Opening batch of 10 streams (total: 130)...
  WARNING: 5 stream(s) were reset by server
  Stream limit enforcement detected

============================================================
STREAM LIMIT TEST RESULTS
============================================================

Server Configuration:
  Advertised max streams:  128

Test Statistics:
  Successful stream opens: 130
  Failed stream opens:     0
  Streams reset by server: 5
  Actual max achieved:     125
  Test duration:           3.45s

Enforcement:
  Stream limit enforcement: DETECTED

============================================================
ASSESSMENT
============================================================

Advertised limit (128) is within recommended range
Server actively enforces stream limits
  Stream limit protection is working correctly
============================================================

7. Interpreting Different Scenarios

7.1. Scenario 1: Proper Enforcement

Advertised max streams:  100
Successful stream opens: 105
Streams reset by server: 5
Actual max achieved:     100
Stream limit enforcement: DETECTED

Analysis: Server properly enforces the limit. Configuration is working exactly as expected.

7.2. Scenario 2: No Enforcement

Advertised max streams:  128
Successful stream opens: 200
Streams reset by server: 0
Actual max achieved:     200
Stream limit enforcement: NOT DETECTED

Analysis: Server accepts far more streams than advertised. This is a potential vulnerability that should be investigated.

7.3. Scenario 3: No Advertised Limit

Advertised max streams:  Not specified
Successful stream opens: 200
Streams reset by server: 0
Actual max achieved:     200
Stream limit enforcement: NOT DETECTED

Analysis: Server does not advertise or enforce limits. High risk configuration that requires immediate remediation.

7.4. Scenario 4: Conservative Limit

Advertised max streams:  50
Successful stream opens: 55
Streams reset by server: 5
Actual max achieved:     50
Stream limit enforcement: DETECTED

Analysis: Very conservative limit. Good for security but may impact performance for legitimate high-throughput applications.

8. Monitoring During Testing

8.1. Server Side Monitoring

While running tests, monitor your server for resource utilization and connection metrics.

Monitor connection states:

netstat -an | grep :443 | awk '{print $6}' | sort | uniq -c

Count active connections:

netstat -an | grep ESTABLISHED | wc -l

Count SYN_RECV connections:

netstat -an | grep SYN_RECV | wc -l

Monitor system resources:

top -l 1 | head -10

8.2. Web Server Specific Monitoring

For Nginx, watch active connections:

watch -n 1 'curl -s https://localhost/nginx_status | grep Active'

For Apache, monitor server status:

watch -n 1 'curl -s https://localhost/server-status | grep requests'

Check HTTP/2 connections:

netstat -an | grep :443 | grep ESTABLISHED | wc -l

Monitor stream counts (if your server exposes this metric):

curl -s https://localhost:9090/metrics | grep http2_streams

Monitor CPU and memory:

top -l 1 | grep -E "CPU|PhysMem"

Check file descriptors:

lsof -i :443 | wc -l

8.3. Using tcpdump

Monitor packets in real time:

# Watch SYN packets
sudo tcpdump -i en0 'tcp[tcpflags] & tcp-syn != 0' -n

# Watch RST packets
sudo tcpdump -i en0 'tcp[tcpflags] & tcp-rst != 0' -n

# Watch specific host and port
sudo tcpdump -i en0 host example.com and port 443 -n

# Save to file for later analysis
sudo tcpdump -i en0 -w test_capture.pcap host example.com

8.4. Using Wireshark

For detailed packet analysis:

# Install Wireshark
brew install --cask wireshark

# Run Wireshark
sudo wireshark

# Or use tshark for command line
tshark -i en0 -f "host example.com"

9. Remediation Steps

If your tests reveal issues, apply these configuration fixes:

9.1. Nginx Configuration

http {
    # Set conservative concurrent stream limit
    http2_max_concurrent_streams 100;

    # Additional protections
    http2_recv_timeout 10s;
    http2_idle_timeout 30s;
    http2_max_field_size 16k;
    http2_max_header_size 32k;
}

9.2. Apache Configuration

Set in httpd.conf or virtual host configuration:

# Set maximum concurrent streams
H2MaxSessionStreams 100

# Additional HTTP/2 settings
H2StreamTimeout 10
H2MinWorkers 10
H2MaxWorkers 150
H2StreamMaxMemSize 65536

9.3. HAProxy Configuration

defaults
    timeout http-request 10s
    timeout http-keep-alive 10s

frontend fe_main
    bind :443 ssl crt /path/to/cert.pem alpn h2,http/1.1

    # Limit streams per connection
    http-request track-sc0 src table connection_limit
    http-request deny if { sc_conn_cur(0) gt 100 }

9.4. Envoy Configuration

static_resources:
  listeners:
  - name: listener_0
    address:
      socket_address:
        address: 0.0.0.0
        port_value: 443
    filter_chains:
    - filters:
      - name: envoy.filters.network.http_connection_manager
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
          http2_protocol_options:
            max_concurrent_streams: 100
            initial_stream_window_size: 65536
            initial_connection_window_size: 1048576

9.5. Caddy Configuration

example.com {
    encode gzip

    # HTTP/2 settings
    protocol {
        experimental_http3
        max_concurrent_streams 100
    }

    reverse_proxy localhost:8080
}

10. Combining with Rapid Reset Testing

You can use both the stream limit tester and the Rapid Reset tester together for comprehensive HTTP/2 security assessment:

# Step 1: Test stream limits
python3 http2_stream_limit_tester.py --host example.com

# Step 2: Test rapid reset with IP spoofing
sudo python3 http2rapidresettester_macos.py \
    --host example.com \
    --cidr 192.168.1.0/24 \
    --packets 1000

# Step 3: Re-test stream limits to verify no degradation
python3 http2_stream_limit_tester.py --host example.com

11. Security Best Practices

11.1. Configuration Guidelines

Set explicit limits: Never rely on default values
Use conservative values: 100-128 streams is the recommended range
Monitor enforcement: Regularly verify that limits are actually being enforced
Document settings: Maintain records of your stream limit configuration
Test after changes: Always test after configuration modifications

11.2. Defense in Depth

Stream limits should be one layer in a comprehensive security strategy:

Stream limits: Prevent excessive concurrent streams per connection
Connection limits: Limit total connections per IP address
Request rate limiting: Throttle requests per second
Resource quotas: Set memory and CPU limits
WAF/DDoS protection: Use cloud-based or on-premise DDoS mitigation

11.3. Regular Testing Schedule

Establish a regular testing schedule:

Weekly: Automated basic stream limit tests
Monthly: Comprehensive security testing including Rapid Reset
After changes: Always test after configuration or infrastructure changes
Quarterly: Full security audit including penetration testing

12. Troubleshooting

12.1. Common Errors

Error: “SSL: CERTIFICATE_VERIFY_FAILED”

This occurs when testing against servers with self-signed certificates. For testing purposes only, you can modify the script to skip certificate verification (not recommended for production testing).

Error: “h2 library not installed”

Install the required library:

pip3 install h2 hyper --break-system-packages

Error: “Connection refused”

Verify the port is open:

telnet example.com 443

Check if HTTP/2 is enabled:

curl -I --http2 https://example.com

Error: “HTTP/2 not negotiated”

The server may not support HTTP/2. Verify with:

curl -I --http2 https://example.com | grep -i http/2

12.2. No Streams Being Reset

If streams are not being reset despite exceeding the advertised limit:

Server may not be enforcing limits properly
Configuration may not have been applied (restart required)
Server may be using a different enforcement mechanism
Limits may be set at a different layer (load balancer vs web server)

12.3. High Failure Rate

If many streams fail to open:

Network connectivity issues
Firewall blocking requests
Server resource exhaustion
Rate limiting triggering prematurely

13. Understanding the Attack Surface

When testing your infrastructure, consider all HTTP/2 endpoints:

Web servers: Nginx, Apache, IIS
Load balancers: HAProxy, Envoy, ALB
API gateways: Kong, Tyk, AWS API Gateway
CDN endpoints: CloudFlare, Fastly, Akamai
Reverse proxies: Traefik, Caddy

13.1. Testing Strategy

Test at multiple layers:

# Test CDN edge
python3 http2_stream_limit_tester.py --host cdn.example.com

# Test load balancer directly
python3 http2_stream_limit_tester.py --host lb.example.com

# Test origin server
python3 http2_stream_limit_tester.py --host origin.example.com

14. Conclusion

Testing your HTTP/2 maximum concurrent streams configuration is essential for maintaining a secure and performant web infrastructure. This tool allows you to:

Verify that your server advertises appropriate stream limits
Confirm that advertised limits are actually enforced
Identify misconfigurations before they can be exploited
Tune performance while maintaining security

Regular testing, combined with proper configuration and monitoring, will help protect your infrastructure against HTTP/2-based attacks while maintaining optimal performance for legitimate users.

15. Additional Resources

This guide and testing script are provided for educational and defensive security purposes only. Always obtain proper authorization before testing systems you do not own.