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Asked: 2026-06-14T18:27:46+00:00

I’ve got a little program that needs to communicate between two computers on the

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I’ve got a little program that needs to communicate between two computers on the same LAN. I’m rather new to networking, but from what I’ve read it sounds like I want UDP multicasting so that the two computers can discover each other, after which I can establish a TCP connection for actual data communication. I’ve found this little example for UDP multicasting which I can follow. However, I’m wondering about the multicast group (HELLO_GROUP in that example, which is 225.0.0.37).

How can I know the group I should use? This program will be running on various networks, so I can’t hard code one (as far as I know). Do I get the group from the router, and if so, how do I do that?

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  1. Editorial Team

    You can choose any multicast address (224.0.0.0 to 239.255.255.255) that isn’t listed as reserved by IANA.

    Its possible (if unlikely) that another program will also be using the same address. You can minimise the chances of this causing any confusion by making the announcement messages your program sends out suitably specific. e.g.

    CORNSTALKS-DISCOVERY
HOST: {address:port}
[newline]

    This would inform your recipients of the address to use for their TCP connection but should find its first line rejected by any other recipients.

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