CODEWITHSUNDEEP
pythonlinuxpython-3.xiptables
user4960960
user4960960

Reputation:

Python/iptables: Original Destination IP

I'm trying to get original destination information for packets redirected with iptables (the ultimate goal is to redirect all network traffic to localhost while retaining the original destination ip).
I'm sending packets using the following code:

import socket  
HOST = '192.168.10.1'
PORT = 50007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.send(b'whatever')
s.close()

Then redirecting it with: 

iptables -t nat -A OUTPUT -d 192.168.10.1 -j DNAT --to 127.0.0.1

And then receiving them with: 

import socket
HOST = ''
PORT = 50007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
while True:
    s.listen(5)
    conn, addr = s.accept()
    print('Connected by', addr)
    data = conn.recv(1024)
    if(data):
        print(data)
conn.close()

I tried using something like 

dst = conn.getsockopt(socket.SOL_IP, socket.SO_ORIGINAL_DST, 16)

but this results in 

AttributeError: 'module' object has no attribute 'SO_ORIGINAL_DST'

Upvotes: 4

Views: 1370

Answers (1)

user4960960
user4960960

Reputation:

Some further reading and trying led me to my mistake. I got a little confused with various approaches I read about and lost track. The clue was in defining SO_ORIGINAL_DST (in this case for TCP).
This code (taken from here) does exactly what I want: 

SO_ORIGINAL_DST = 80
sockaddr_in = conn.getsockopt(socket.SOL_IP,
                              SO_ORIGINAL_DST, 16)
(proto, port, a, b, c, d) = struct.unpack('!HHBBBB', sockaddr_in[:8])
print('Original destination was: %d.%d.%d.%d:%d' % (a, b, c, d, port))

Upvotes: 3

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