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Editorial Team
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Asked: 2026-05-26T04:09:08+00:00

I’m trying to find a way for client to know socket server ip:port, without

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I’m trying to find a way for client to know socket server ip:port, without explicitly defining it. Generally I have a socket server running on portable device that’s connect to network over DHCP (via WiFi), and ideally clients should be able to find it automaticaly.

So I guess a question is whether socket server can somehow broadcast it’s address over local network? I think UPnP can do this, but I’d rather not get into it.

I’m quite sure that this question was asked on Stack lot’s of times, but I could find proper keywords to search for it.

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1 Answer

  1. Editorial Team

    One method of doing this is via UDP broadcast packets. See beej’s guide if you’re using BSD sockets. And here is Microsoft’s version of the same.

    Assuming all the clients of the application are on the same side of a router then a broadcast address of 255.255.255.255 (or ff02::1 for IPv6) should be more than adequate.

    Multicast is another option, but if this is a LAN-only thing I don’t think that’s necessary.

    Suggestion

    Pick a UDP port number (say for the sake of an example we pick 1667). The client should listen to UDP messages on 255.255.255.255:1667 (or whatever the equivalent is. e.g.: IPEndPoint(IPAddress.Any, 1667)). The server should broadcast messages on the same address.

    Format Suggestion

    UDP Packet: First four bytes as a magic number, next four bytes an IPv4 address (and you might want to add other things like a server name).

    The magic number is just in case there is a collision with another application using the same port. Check both the length of the packet and the magic number.

    Server would broadcast the packet at something like 30 second time intervals. (Alternatively you could have the server send a response only when a client sends a request via broadcast.)

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