wiki.millerjs.org

I guess rebroadcaster isn't quite the right term, but what this script does is capture a TCP stream from a mirrored switch port and make it available on a local socket for use by other tools. For example, streaming to an NTRIP mountpoint.

Deploying this script has a few requirements. In my example, a network device with IP address 172.16.0.108 is transmitting a TCP stream on port 2201. On the switch this device is connected to, its port is mirrored to another, so any traffic sent or received by that device can be transparrently rebroadcasted to another device. You'll need another device with a network interface that supports being run in promiscious mode so that it can capture the traffic. This should be separate from its primary network interface. The second network interface will need to be put into promiscious mode - an example systemd service definition is provided below.

promisc-enp2s0.service

[Unit]
Description=Control promiscuous mode for interface enp2s0
After=network.target
 
[Service]
Type=oneshot
ExecStart=/usr/bin/ip link set enp2s0 up
ExecStart=/usr/bin/ip link set enp2s0 promisc on
ExecStop=/usr/bin/ip link set enp2s0 promisc off
RemainAfterExit=yes
 
[Install]
WantedBy=multi-user.target

sniffedstream2newstream.service

[Unit]
Description=Hyfix2TCPStream
After=network.target
Wants=network-online.target
After=network-online.target
 
[Service]
ExecStart=/usr/bin/hyfix2tcpstream.py
Restart=always
RuntimeMaxSec=43200
RestartSec=10
TimeoutStartSec=30
User=root
 
[Install]
WantedBy=default.target

sniffedstream2newstream.py

#!/usr/bin/env python3
 
import socket
import sys
import signal
import threading
from scapy.all import sniff, IP, TCP
 
# Capture Configuration
CAPTURE_INTERFACE = "enp2s0"  # Your promiscuous interface
SOURCE_IP = "172.16.0.108"    # Source IP of the device sending data
TARGET_PORT = 2201            # The port you're capturing
LOCAL_PORT = 3000             # Local port to serve the captured data on
 
# Global variables
clients = []
clients_lock = threading.Lock()
 
def signal_handler(sig, frame):
    print('Stopping capture and closing connections...')
    # Close local client connections
    with clients_lock:
        for client in clients:
            try:
                client.close()
            except:
                pass
    sys.exit(0)
 
def packet_handler(packet):
    """Process each captured packet and forward its payload"""
    if IP in packet and TCP in packet:
        if packet[IP].src == SOURCE_IP and packet[TCP].dport == TARGET_PORT:
            if packet[TCP].payload:
                payload = bytes(packet[TCP].payload)
                if payload:
                    # Forward payload to all connected clients
                    with clients_lock:
                        disconnected = []
                        for client in clients:
                            try:
                                client.sendall(payload)
                            except:
                                disconnected.append(client)
 
                        # Remove disconnected clients
                        for client in disconnected:
                            clients.remove(client)
 
def client_handler(client_socket, addr):
    """Handle a connected client"""
    print(f"New client connected: {addr}")
    with clients_lock:
        clients.append(client_socket)
 
    # Keep connection open until client disconnects
    try:
        while True:
            data = client_socket.recv(1024)
            if not data:
                break
    except:
        pass
    finally:
        with clients_lock:
            if client_socket in clients:
                clients.remove(client_socket)
        client_socket.close()
        print(f"Client disconnected: {addr}")
 
def start_server():
    """Start a TCP server to serve captured data"""
    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server.bind(('0.0.0.0', LOCAL_PORT))
    server.listen(5)
    print(f"Listening for connections on port {LOCAL_PORT}")
 
    while True:
        client_sock, address = server.accept()
        client_thread = threading.Thread(target=client_handler, args=(client_sock, address))
        client_thread.daemon = True
        client_thread.start()
 
if __name__ == "__main__":
    # Set up signal handler for clean shutdown
    signal.signal(signal.SIGINT, signal_handler)
 
    # Start TCP server in a separate thread
    server_thread = threading.Thread(target=start_server)
    server_thread.daemon = True
    server_thread.start()
 
    print(f"Starting payload capture from {SOURCE_IP}:{TARGET_PORT}")
    print(f"Sniffing on {CAPTURE_INTERFACE}...")
 
    # Start packet capture
    sniff(
        iface=CAPTURE_INTERFACE,
        filter=f"tcp and src host {SOURCE_IP} and dst port {TARGET_PORT}",
        prn=packet_handler,
        store=0
    )