March 23rd, 2004, 09:44 AM
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DNS/BIND Guru
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Join Date: Jun 2003
Location: OH, USA
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You can use any source port for your UDP request. The only problem is if you have a simple firewall with no intelligence to let the DNS UDP responses through. Here's some of the code of my own resolver written in pure C (not C++):
In this example I don't even bind to a local port. I just let the system select one automatically since I have no firewall issues.
Code:
//create a socket for UDP
if (!(s = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP)))
return 0;
//store the remote address info
sockaddr.sin_family = AF_INET;
sockaddr.sin_port = 0x3500; //port 53
memcpy(&sockaddr.sin_addr, &addr, 4);
//send the packet to the server
if (sendto(s, query, size+5, 0, (SOCKADDR*)&sockaddr, sizeof(SOCKADDR)) == SOCKET_ERROR) {
printf("Failed to send packet\n");
closesocket(s);
return 0;
}
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