DNS Query

[Rij]

Hi,

I am trying to write a program that will do automatic DNS query. I use two approaches. When I ask the system to build the query for me using "res_query", it works fine. But when I try to build the query by making the library call "res_mkquery", it doesn't. Specifically, the program hangs waiting for a response from the DNS server. Any help will be greatly appreciated. Here is the code.


int main() {
struct sockaddr_in to_addr;
char udp_query[200], udp_response[200], domain_name[] = "www.google.com";
int s_sock, tx_id, s_tx_id, flags, byte_count;
ushort s_flag = 0x0100, r_flag = 0x8180;
socklen_t sin_len;

to_addr.sin_family = AF_INET;
to_addr.sin_port = 53;
if (inet_aton("10.10.10.10", &(to_addr.sin_addr)) <=0) {
printf("Invalid address.\n");
return 0;
}

s_sock = socket(AF_INET, SOCK_DGRAM, 0);
if (s_sock < 0) {
printf("udp socket: %s", strerror(errno));
return 0;
}

byte_count = res_mkquery(QUERY, domain_name, C_IN, T_ANY, NULL, 0,
NULL, udp_query, 190);
if (byte_count == -1) {
printf("Couldn't make DNS query: %s", strerror(errno));
}
printf("Query size = %d\n", byte_count);

s_tx_id = get_uint16(udp_query);
flags = get_uint16(udp_query+2);

if (flags != s_flag) {
printf("Malformed DNS query\n");
return 0;
}

printf("Sending ...\n");

byte_count = sendto(s_sock, udp_query, byte_count, MSG_DONTWAIT,
(struct sockaddr *)&to_addr, sizeof(to_addr));

if (byte_count < strlen(udp_query)) {
printf("UDP packet send error: %s", strerror(errno));
return 0;
}

printf("Bytes sent = %d, destination = %s\n", byte_count, inet_ntoa(to_addr.sin_addr.s_addr));

printf("Waiting ...\n");

byte_count = recvfrom(s_sock, udp_response, 190, 0,
(struct sockaddr *)&to_addr, &sin_len);
if (byte_count <= 0) {
printf("udp recvfrom on socket = %d: %s", s_sock, strerror(errno));
return 0;
}

/*if (res_query(domain_name, C_IN, T_ANY, udp_response, sizeof(udp_response)) < 0) {
printf("Error: %s\n", strerror(errno));
return 0;
}*/

printf("Will check ...\n");

s_tx_id = tx_id = get_uint16(udp_response);
flags = get_uint16(udp_response+2);

if ((tx_id == s_tx_id) && (flags == r_flag)) {
printf("Matched.\n");
}
}

[stroyan]

strace of the system calls shows that the port is wrong.

Change
to_addr.sin_port = 53;
to
to_addr.sin_port = htons(53);

[Rij]

Ah! Thanks!

[kuttya]

If you need DNS query means try this site http://www.whoisxy.com/ and also get the ip to domain,domain to ip,ping test,etc......

[Phoenixie]

If you need DNS query means try this site http://www.whoisxy.com/ and also get the ip to domain,domain to ip,ping test,etc......

Nice, bumping one year old thread to promote your crappy website.

[Ravenshade]

...guess this also counts as a bump.

He probably did the same thing as me and searched for it but didn't notice the last time the topic had been replied to. Now....MOD! Shouldn't this thread be locked?