Python Port Scanner

Question

Am newbie to python and stuck at a point. I want to create port scanner with using only python 3 inbuilt libraries (means avoiding scapy etc) I have following code :

import socket
for i in range(1,26):  
  s = socket.socket()  
  s.settimeout(0.5)
  ip = "74.207.244.221" #scanme.nmap.org
  response = s.connect_ex((ip, i)) 
  if response:
      print ("%d\tclose" %i)
  else:
      print ("%d\topen" %i)
  s.close()

Now I want to add 2 functionalities to this : that is

1. Distinguish between close and filtered ports . In both cases am receiving same errno in return so how can I check if I have received back a rst packet or nothing ? As far as I have tried s.recv() isn't working for this.
2. I want to control the number of tries (attempts), ie I want to send only one or two syn packets. I don't want this program to send more than 2 syn packets for probes. How can this thing be achieved ?

Answer 1

Distinguish between close and filtered ports . In both cases am receiving same errno in return so how can I check if I have received back a rst packet or nothing

You've probably only checked with servers that send back a RST. Here's what I tried:

• First case, normal config:

   >>> os.strerror(s.connect_ex((ip, 81))) 'Connection refused' 

• Second, with manual iptables:

   iptables -A OUTPUT -p tcp --dport 81 -j DROP >>> os.strerror(s.connect_ex((ip, 81))) 'Resource temporarily unavailable' 

I want to control the number of tries (attempts), ie I want to send only one or two syn packets.

I don't think there's a setsockopt TCP option exposed, but on linux there's:

net.ipv4.tcp_syn_retries

However, since you limited the timeout for the socket, all operations that don't finish within 0.5 seconds will time out. So it's likely only 1 or 2 SYNs will leave the station.

Answer 2

#!/usr/bin/python

import socket

s = socket.socket(socket.AF_INET, socekt.SOCK_STREAM)
host = 74.207.244.221

def portscan(port):
    try:
        s.connect((host,port))
        return True
    else:
        return False
for x in range(1,255):
    if portscan(x):
        print('Port',x,'Is Open')