Test all outbound TCP/UDP ports for connectivity to a remote host.

Testing all ports can take 3-10 minutes depending on connection speed.

Can also be used to detect passive DPI Firewalls that block traffic not looking like the expected service for a given port.

• Network troubleshooting: Identify which ports are blocked by firewalls
• Security testing: Test outbound connectivity from restricted networks
• DPI detection: Discover deep packet inspection that blocks non-standard protocols
• Infrastructure validation: Verify port accessibility in cloud/container environments
• Network monitoring: Baseline network connectivity for monitoring

For testing connectivity (any platform):

• Download portquiz for your platform (Windows, macOS, Linux)

For running a server (Linux only):

• Download portquiz-server for Linux

git clone https://github.com/lanrat/portquiz.git
cd portquiz
make

# Test connectivity to a server (most common use case)
./portquiz -tcp -udp example.com

# Test specific ports only
./portquiz -tcp -port 22,80,443 example.com

# Show only open ports
./portquiz -tcp -udp -open example.com

⚠️ WARNING: The server creates iptables rules that redirect ALL incoming traffic to the listening IP. If you use the same IP for remote access (SSH, etc.), YOU WILL BE LOCKED OUT! Always use a dedicated IP address for the server.

Requirements:

• Linux system with iptables
• Root privileges (for firewall rule management)
• Dedicated IP address (separate from management/SSH access)

$ ./portquiz-server -h
Usage of ./portquiz-server:
  -listen string
        comma separated list of IPs to listen on (default "127.0.0.123")
  -no-iptables
        disable automatically creating iptables rules
  -password string
        magicString to use, must be the same on client/server (default "portquiz")
  -port uint
        default port to listen on which will have traffic redirected to (default 1337)
  -tcp
        start TCP server
  -timeout duration
        amount of time for each connection (default 10s)
  -udp
        start UDP server
  -verbose
        enable verbose logging

# start server
# listen on TCP and UDP ports
# listens on IPv4: 192.0.2.123 and IPv6: 2001:0DB8::1
./portquiz-server -tcp -udp -listen 192.0.2.123,2001:0DB8::1

The portquiz client connects to the portquiz server and tests port connectivity. By default portquiz will test all ports unless -port is specified.

Note: The client binary is named portquiz (cross-platform), while the server binary is portquiz-server (Linux only).

IPv4 can be forced with -4 and IPv6 can be forced with -6. If both are provided (-4 -6) then each port is tested using both IPv4 and IPv6. If unspecified, only one protocol version is tested.

$ ./portquiz -h
Usage of ./portquiz:
  -4    force IPv4
  -6    force IPv6
  -closed
        print only closed ports
  -multi uint
        test multiple times to ensure larger streams work (default 1)
  -open
        print only open ports
  -parallel uint
        number of worker threads (default 20)
  -password string
        magicString to use, must be the same on client/server (default "portquiz")
  -port string
        comma separated list of ports to test
  -retry uint
        retry count (default 3)
  -tcp
        start TCP client
  -timeout duration
        amount of time for each connection (default 5s)
  -udp
        start UDP client
  -verbose
        enable verbose logging

# test UDP and TCP ports, only print open ports
./portquiz -tcp -udp -open portquiz.example.com

1. Server Setup: The server listens on a single port and uses iptables DNAT rules to redirect traffic from all ports to this listening port
2. Client Testing: The client attempts to connect to each port and sends a magic string
3. Response Validation: The server responds with the same magic string if the connection is successful
4. Protocol Detection: Can detect DPI firewalls that block connections based on protocol patterns

Client shows all ports as closed:

• Verify the server is running and accessible
• Check that firewall rules are properly configured
• Ensure the magic string matches between client and server

Server setup fails:

• Verify you have root privileges
• Check that iptables is installed and available
• Ensure the listening IP is correctly configured on the system

Performance is slow:

• Reduce parallelism with -parallel flag
• Test specific ports instead of all ports
• Adjust timeout values for faster networks