netcat

nc -nvlp 7777

listening on port 7777

Building a Port Scanner

#!bin/python3

# filename = scanner.pyÍÍ
import sys
import socket
from datetime import datetime 

# defining the target
if len(sys.argv) == 2:
    target = socket.gethostbyname(sys.argv[1]) # translating host name to IPv4
    
else:
    print("Invalid argument")
    print("Syntax: python3 scanner.py <ip>")
    
# add a pretty banner
print("-" * 50)
print("Scanning target " + target)
print("Time started " + str(datetime.now()))
print("-" * 50)

try:
    for port in range(50,85):
        s= socket.socket(socket.AF_INET, socket.SOCK_STREAM) # IPv4 and port
        socket.setdefaultimeout(1) # wait for 1 sec at every port and then move on
        result = s.connect_ex(target,port) # returns an error indicator
        if result == 0:
            print("Port {} is open".format(port))
        s.close()
        
except KeyboardInterrupt:
    print("\nExiting Program.")
    sys.exit()

except socket.gaierror:
    print("\nHost Name couldnot be resolved")
    sys.exit()
    
except socket.error:
    print(\nCouldn't connect to the server")
    sys.exit()