Using TPROXY to bind to any port on many IPs (asyncio variant)

anybind_aio.py

import asyncio
import socket

BIND_IP = "127.0.0.1"
TCP_PORT = 1234
SOCK_BACKLOG = 32
IP_TRANSPARENT = 19

desc = f"""
Anybind; "bind" on many IPs and many Ports.
See: https://blog.cloudflare.com/how-we-built-spectrum/

You may need to configure routing and TPROXY:
sudo ip route add local 192.168.250.0/24 dev lo src {BIND_IP}
sudo iptables -t mangle -I PREROUTING \
-d 192.168.250.0/24 -p tcp \
-j TPROXY --on-port={TCP_PORT} --on-ip={BIND_IP}

Needs: CAP_NET_ADMIN capability
"""


async def handle_echo(_, writer):
    try:
        data = b"I'm everywhere.'\n"
        s_ip, s_port = writer.get_extra_info('peername')
        d_ip, d_port = writer.get_extra_info('sockname')
        print(f"Conn tcp://{s_ip}:{s_port} → tcp://{d_ip}:{d_port}")

        writer.write(data)
        writer.write_eof()
        await writer.drain()
    except ConnectionResetError:
        print("Conn: RIP")
    finally:
        print("Close the client socket")
        writer.close()


s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.setsockopt(socket.IPPROTO_IP, IP_TRANSPARENT, 1)
s.bind((BIND_IP, TCP_PORT))
s.listen(SOCK_BACKLOG)
loop = asyncio.get_event_loop()
coro = asyncio.start_server(handle_echo, sock=s, loop=loop)
server = loop.run_until_complete(coro)

# Serve requests until Ctrl+C is pressed
b_ip, b_port = server.sockets[0].getsockname()
print(desc)
print(f'Serving on tcp://{b_ip}:{b_port}')
try:
    loop.run_forever()
except KeyboardInterrupt:
    pass

print("Close server")
server.close()
loop.run_until_complete(server.wait_closed())
loop.close()