Python port forwarding/multiplexing server

Question

I would like to make server that listen on UDP port 162 (SNMP trap) and then forwards this traffic to multiple clients. Also important is that the source port & address stays same (address spoofing).

I guess that best tool for this would be Twisted or Scapy or maybe vanilla sockets, only I can't find anything in the documentation for Twisted about source address spoofing/forging.

Any solution for this?

Edit:added bounty, mybe any solution with iptables?

Answer 1

I am not comfortable with twisted or scapy, but it's quite straightforward to do this with vanilla python sockets. An extra advantage of that is that it will be even more portable. This code works in my limited tests:

#!/usr/bin/python
from socket import *
bufsize = 1024 # Modify to suit your needs
targetHost = "somehost.yourdomain.com"
listenPort = 1123

def forward(data, port):
    print "Forwarding: '%s' from port %s" % (data, port)
    sock = socket(AF_INET, SOCK_DGRAM)
    sock.bind(("localhost", port)) # Bind to the port data came in on
    sock.sendto(data, (targetHost, listenPort))

def listen(host, port):
    listenSocket = socket(AF_INET, SOCK_DGRAM)
    listenSocket.bind((host, port))
    while True:
        data, addr = listenSocket.recvfrom(bufsize)
        forward(data, addr[1]) # data and port

listen("localhost", listenPort)