Re: Newbie: Keep TCP socket open

Discussion in 'Python' started by s0suk3@gmail.com, May 19, 2008.

  1. Guest

    On May 19, 10:25 am, "Alan Wright" <> wrote:
    > Hi Folks,
    > I am newbie to Python, but have successfully created a simple client and
    > server setup, I have one issue though.
    >
    > I am trying to test a box by sending many TCP conns (WHILE loop) but not
    > closing them with a FIN/RST. However, no matter what i do, i cannot get the
    > loop to stop sending FIN from the client.
    >
    > Any clues?
    >
    > Here is my current script
    >
    > #!/usr/bin/python
    >
    > import socket,sys
    > from numpy import *
    > num1=0
    >
    > while (num1<=10) :
    >
    > s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    > s.settimeout(10.0)
    > s.connect(("10.1.1.69", 50008)) # SMTP
    > print s.recv(1024) + '\n',
    > num1=num1+1
    > #s.close()
    >
    > sys.exit(1)


    socket.socket instances do an implicit close() on the socket when the
    object is destructed (in this case, it's destructed when it is garbage-
    collected). What's happening is that on each iteration, the variable
    "s", which references the socket.socket instance, is assigned to a new
    socket.socket instance, therefore the instance of the previous
    iteration is no longer referenced by "s", and since it's no longer
    referenced by anything, the instance is garbage-collected,
    automatically imposing an implicit close() on that instance. A simple
    solution could be to create a list and append the socket.socket
    instance of each iteration to that list, that way the instances would
    remain referenced in the list and not be garbage-collected; though you
    might be able to find a more elegant solution.

    Sebastian
     
    , May 19, 2008
    #1
    1. Advertising

  2. Ghirai Guest

    On Mon, 19 May 2008 20:25:57 +0100
    "Alan Wright" <> wrote:

    > Thanks for the feedback.
    >
    > Using the socket in a list is great
    >
    > However, as i imagined, I now get a limit of around 1500 conns before
    > the system crashes out, also i have noticed, that the ports loop back
    > to 1025 when they hit 5000.
    >
    > Any ideas on how to make the list/socket get to around 50K
    >
    > TIA
    >


    Try to use scapy to send raw empty packets with S flag set.
    Also use Linux/BSD if you're trying this on Windows.

    --
    Regards,
    Ghirai.
     
    Ghirai, May 19, 2008
    #2
    1. Advertising

  3. Ghirai Guest

    On Mon, 19 May 2008 23:50:50 +0100
    "Alan Wright" <> wrote:

    > Ghirai,
    > Scapy does the same, only it sends RST and not FIN, so still no help
    >
    > send(IP(dst="10.1.1.2")/TCP(dport=50000,flags="S"))
    >
    > Only have windows at the moment sadly.
    >
    > Alan
    >


    Are you sure there's no firewall or something else between you and the
    remote host?

    Because i just tried that command with scapy and it didn't send any other packets
    except what it was told (1 packet with SYN flag set).

    I haven't tried on windows though.

    --
    Regards,
    Ghirai.
     
    Ghirai, May 20, 2008
    #3
  4. Roy Smith Guest

    In article <>,
    "Alan Wright" <> wrote:

    > Thanks for the feedback.
    >
    > Using the socket in a list is great
    >
    > However, as i imagined, I now get a limit of around 1500 conns before the
    > system crashes out, also i have noticed, that the ports loop back to 1025
    > when they hit 5000.
    >
    > Any ideas on how to make the list/socket get to around 50K


    Yikes. Not on any box I know of. A given process is limited in how many
    descriptors it can have open at once. I don't know of any that will allow
    anywhere near 50k. Somewhere in the 1-2000 range would be more typical.
    The 1500 you report is not at all surprising.

    You might try creating a bunch of child processes with os.system() or
    something of that ilk. Create 50 processes and have each one open 1000
    sockets.

    The next thing you have to worry about is whether the OS can handle 50k
    file descriptors open per-system. Or 50k sockets, or TCP connections. I
    wouldn't be too surprised if many systems couldn't. The address space (TCP
    port numbers) is 16-bit (unsigned), or about 65k, but you may well run into
    some other system limit long before you exhaust the theoretically available
    ports.

    Something like Scapy, recommended by others, may indeed be able to generate
    all those SYN packets you want, but that doesn't mean you'll get all the
    open connections you seek. You send a SYN packet to the remote host, and
    it sends back a SYN/ACK. The local kernel now sees a SYN/ACK packet for a
    port it doesn't know about. I'm not sure what the RFCs say about that, but
    I wouldn't be surprised if the kernel ends up sending a RST or maybe a FIN
    or something like that. The kernel owns the ports; it's not nice to try
    and mess with them on your own.
     
    Roy Smith, May 20, 2008
    #4
  5. Roy Smith Guest

    In article <>,
    "Alan Wright" <> wrote:

    > Thanks Roy
    >
    > Any ideas how to code this child process stuff, as I said I am newbie and
    > not from a coding background


    The easiest thing would be to use os.system(). If you wanted to spawn 10
    child processes, you could do:

    import os
    for i in range(10):
    os.system ("./child.py &")

    and then have child.py be a script that creates 1000 TCP connections.

    Keep in mind that one man's stress test is another man's denial of service
    attack. If there are any firewalls between you and your target, they may
    restrict the number of connections you get to make (or the rate at which
    they're created). You may also get a polite phone call from your local IT
    people asking enquiring about your activities.
     
    Roy Smith, May 21, 2008
    #5
  6. Roy Smith Guest

    In article <>,
    "Alan Wright" <> wrote:

    > infact there is no need for any IT phone calls, I am the owner of this
    > network


    That's the best way to do it :)
     
    Roy Smith, May 21, 2008
    #6
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. pwilkins
    Replies:
    7
    Views:
    482
    Grant Edwards
    Jun 25, 2005
  2. Tiger
    Replies:
    5
    Views:
    1,011
    Dave Thompson
    May 1, 2006
  3. TCP Socket login handling. Newbie

    , Jul 15, 2006, in forum: C Programming
    Replies:
    0
    Views:
    373
  4. Irmen de Jong

    Re: Newbie: Keep TCP socket open

    Irmen de Jong, May 19, 2008, in forum: Python
    Replies:
    0
    Views:
    553
    Irmen de Jong
    May 19, 2008
  5. hisan
    Replies:
    1
    Views:
    1,415
    Dan Stromberg
    Jun 25, 2012
Loading...

Share This Page