Thread: UDP programming - set local port

  1. #1
    Registered User
    Join Date
    Jan 2003

    UDP programming - set local port

    Is there a way to specify a particular port for UDP sockets to send packets *out* of? I've tried using bind(), and it does in fact seem to bind the socket (using netstat to check), but using sendto() the packets are still sent from an arbitrary port. I don't have all that much experience with UDP, but that seems strange....

    Any help would be appreciated.

  2. #2
    Registered User
    Join Date
    Sep 2004
    Yes I also Have this problem, I can send udp packets to a server, But how to I specify the port for the client to use. Rather than any old random one thats free. Info Im finding info mainly releated to server side.

  3. #3
    Its not rocket science vasanth's Avatar
    Join Date
    Jan 2002
    struct sockaddr_in sa;
    memset(&sa, 0, sizeof(sa));
    sa.sin_port = htons( port );
    considering the above code i think your code will be having something like sa.sin_port = htons(0); where 0 tells it to use any random port.. You can specify your own port here instead of 0 to use your custom specified port..

  4. #4
    Registered User
    Join Date
    Mar 2003

    I have a question regarding UDP Communications.
    What is necessary to make the built-in Fastnet NMUDP component (Borland C++ Builder 5) work?

    There are 3 PCs at home, the Borland C++ Builder is installed on each one. Each has Windows XP, SP2, but my programs using this NMUDP component are only working on 2 of the PCs.
    It seems that there's no UDP communications allowed on that PC at all! I checked the firewalls, the router, etc. but the UDP is not forbidden anywhere.

    I tested my program on other PCs too, with Windows2000. That was quit interesting too. Those PCs were on a LAN about which I don't have detailed information. On those PCs reception of the UDP packets worked, but they couldn't send packets to my notebook.

    Does anybody have an idea what could be the issue?

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