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Editorial Team
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Asked: 2026-06-14T01:42:56+00:00

As an example, suppose I have a ‘smart’ thermometer that broadcasts the current temperature

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As an example, suppose I have a ‘smart’ thermometer that broadcasts the current temperature as a UDP datagram every N seconds.

Now, I can write a client that listens for those messages and displays them graphically, and I can have that client running on multiple computers simultaneously. No problem so far.

But, when I try to run two instances of the client on the same Windows computer, I get errors about attempting to “bind to a port already in use“.

Is this:-

  • A: Just the way it is with UDP broadcasts, on all operating systems?
  • B: a limitation of the Windows networking stack?
  • C: or, probably a bug in the way I’m reading the datagrams?

If A or B, is there any way round it.

If C, then I’ll post some code..

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1 Answer

  1. Editorial Team

    On Windows you can have multiple processes bind to the same socket by using the

    SocketOptionName.ReuseAddress

    option (see this answer Is there a way for multiple processes to share a listening socket?). Broadcasting a packet should force Windows to give a copy of that packet to each listener on that end-point.

    In answer to Roddy, yes, SO_REUSEADDR works this way on *nix too.

    For in-depth answer, refer to https://stackoverflow.com/a/14388707/705086.

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