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Question about network ports RRS feed

  • Question

  • Hi

    I would like to clear something for myself in regard to "Network Ports". 

    Let's say I have an FTP server and I've changed the port so it listens on port "7000". I have a friend who is running an FTP server which is configured on port 21. 

    If I transfer a file from my FTP server, will my friend receive my file? And if my friend sends me his file, will I receive his file? 

    To my understanding, the answer would be "No" to both of my questions because my FTP server is configured on port 7000 while my friends server configured on port 21. To receive/send a file to and from another FTP server, he will need to be configured his FTP server to operate on port 7000. 

    Thanks 

    Sunday, May 28, 2017 10:46 AM

Answers

All replies

  • Hi,

    nice nick ;-)

    FTP file transfers are not from server to server but from server to client or vice versa. The communication is initiated by the client which, of course, needs to know which port the server service is listening on. But the port the client is using for opening a connection needs not be the same as the server port and is mostly randomly selected from the upper range.

    So if your friend wants to request a file from your FTP server, he will have to specify port 7000 going forward. If you want to send a file to your friend's FTP server (which hastn't been modified) you can continue using the default port (i.e. omitting a specific value).


    Evgenij Smirnov

    I work @ msg services ag, Berlin -> http://www.msg-services.de
    I blog (in German) @ http://it-pro-berlin.de
    my stuff in PSGallery --> https://www.powershellgallery.com/profiles/it-pro-berlin.de/
    Exchange User Group, Berlin -> http://exusg.de
    Windows Server User Group, Berlin -> http://www.winsvr-berlin.de
    Mark Minasi Technical Forum, reloaded -> http://newforum.minasi.com

    • Marked as answer by V PIZDU Sunday, May 28, 2017 10:18 PM
    • Unmarked as answer by V PIZDU Sunday, May 28, 2017 11:38 PM
    • Marked as answer by V PIZDU Sunday, May 28, 2017 11:38 PM
    Sunday, May 28, 2017 3:23 PM
  • Hello Evgeni

    Thanks for your reply. Yeah, the nick is funny but stupid...  

    ( ͡° ͜ʖ ͡°)

    What about Exchange server. Let's say I change my port from 25 to 7001 and my friend "Bob" is still using port 25. I would assume communiucaton between my mail server and Bob's mail server will not work since all mail servers are configured to listen on port 25. Unless Bob configures his Exchange server to receive and send on port 7001. Is that correct? And yes, I do understand that I will need to open a firewall rule that listens SMPT to port 7001. 

    Cheers 


    Sunday, May 28, 2017 10:18 PM
  • Hi,

    again, in a SMTP hop-to-hop scenario, the sending server acts as a client and yes, it needs to know if the next hop expects a non-default port to be used.

    In Exchange, this would be a separate send connector on Bob's side scoped to your SMTP domain where Bob would specify your mail server as next hop including Port 7001.

    And yes, to accept incoming communications on that port it would need to be open on the firewall.


    Evgenij Smirnov

    I work @ msg services ag, Berlin -> http://www.msg-services.de
    I blog (in German) @ http://it-pro-berlin.de
    my stuff in PSGallery --> https://www.powershellgallery.com/profiles/it-pro-berlin.de/
    Exchange User Group, Berlin -> http://exusg.de
    Windows Server User Group, Berlin -> http://www.winsvr-berlin.de
    Mark Minasi Technical Forum, reloaded -> http://newforum.minasi.com

    • Marked as answer by V PIZDU Monday, May 29, 2017 10:49 PM
    Monday, May 29, 2017 4:30 AM