title: Python UDP client did not respond
body: <p>A python UDP client:</p>
  
  <pre><code>root@kali-linux:~# python
  Python 2.7.14 (default, Sep 17 2017, 18:50:44) 
  [GCC 7.2.0] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; import socket
  &gt;&gt;&gt; target_host = "127.0.0.1"
  &gt;&gt;&gt; target_port = 80
  &gt;&gt;&gt; client = socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
  &gt;&gt;&gt; client.sendto("AAABBBCCC",(target_host,target_port))
  9
  &gt;&gt;&gt; data, addr = client.recvfrom(4096)
          # to this line,no response
  &gt;&gt;&gt;print data   # waiting for imput
  </code></pre>
  
  <p>when I input "data, addr = client.recvfrom(4096)" then ENTER,I wait for ten minutes that no response.</p>
  
  <p>But when I program a TCP client,it work.This is code:</p>
  
  <pre><code>root@kali-linux:~# python
  Python 2.7.14 (default, Sep 17 2017, 18:55:37) 
  [GCC 7.2.0] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt;import socket
  &gt;&gt;&gt;target_host = "www.baidu.com"
  &gt;&gt;&gt;target_port = 80
  &gt;&gt;&gt;client = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
  &gt;&gt;&gt;client.connect((target_host,target_port))
  &gt;&gt;&gt;client.send("GET / HTTP/1.1\r\nHost: baidu.com\r\n\r\n")
  35
  &gt;&gt;&gt;response = client.recv(4096)
  &gt;&gt;&gt;print response 
  #output
  HTTP/1.1 200 OK
  Date: Thu, 16 Nov 2017 12:05:07 GMT
  Content-Type: text/html
  Content-Length: 14613
  Last-Modified: Wed, 01 Nov 2017 03:00:00 GMT
  Connection: Keep-Alive
  Vary: Accept-Encoding
  
  AND SO ON ..........
  </code></pre>
  
  <p>TCP client can work and UDP client can't work,why?</p>
  
  <p>what should I do?</p>