You need to read up on port scanning. UDP is connectionless ie you can't see if a port is open by seeing if you can connect a socket to it, you have to send some data and check for a response.

Port scanning usually means scanning for TCP ports, which are connection-oriented and therefore give good feedback to the attacker. UDP, or connection-less traffic, responds in a different manner. In order to find UDP ports, the attacker generally sends empty UDP datagrams at the port. If the port is listening, the service will send back an error message or ignore the incoming datagram. If the port is closed, then the operating system sends back an "ICMP Port Unreachable" message.

Note that UDP packets may be dropped by all manner of devices along the way (so you get no response). The response, if it is coming, will arrive on the socket you sent the probe out on as shown. You have to send some sort of valid(ish) UDP packet to incite a response from the server.

NetworkInfo::Discovery::Scan does what you want and you can pull code from there.

cheers

tachyon

In reply to Re^5: udp recv question by tachyon
in thread udp recv question by smackdab

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