I created a socket using: socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP).
According to this, if I send simple packet several times (multiply send() and/or sendto()), I can get ECONNREFUSED. ICMP should tell that previous packet didn't arrive and ECONNREFUSED should appear. But it fails, errno doesn't report about any errors, and send() always returns number of bytes sent.
UDP protocol actually shouldn't tell that packet was sent. But ICMP can give advice as I understand.
So, the question is - why does it fail to receive ECONNREFUSED?
Everything is done using Winsock.
There could be two reasons for this.
- The target machine does not (for some reason) send the
ICMP back
- The target machines does send the
ICMP back but winsock doesn't correctly interpret it (I know that certain older Unixes did this)
In short, your best bet to find out would be using a sniffer. Try wireshark and see if you get an ICMP back.
INFO: Winsock Ignores ICMP Port Unreachable Control Messages
You have to enable the SIO_UDP_CONNRESET control via WSAIoctl() in order for UDP sockets to react to ICMP failures:
WinSock Recvfrom() now returns WSAECONNRESET instead of blocking or timing out
