Extracting DNS info from a captured packet in C

Question

I am using below code from here to print DNS information from captured packets. It perfectly words till I print out the TTL.

packet_desc* pd = (packet_desc*)pack;
printf("IP HEADER\n");  
printf("%ssource:%s\n", tab, inet_ntoa(pd->ip.src) );
printf("%sdest:%s\n", tab, inet_ntoa(pd->ip.dst) );
printf("UDP HEADER\n"); 
printf("%ssource port:%d\n", tab, ntohs(pd->udp.sport) );   
printf("%sdest port:%d\n", tab, ntohs(pd->udp.dport) ); 

printf("DNS HEADER\n");
printf("%sid:%d\n", tab, ntohs(pd->dns.id));
printf("%sflags:%d\n", tab, ntohs(pd->dns.flags));
printf("%s# questions:%d\n", tab, ntohs(pd->dns.qdcount));
printf("%s# answers:%d\n", tab, ntohs(pd->dns.ancount));
printf("%s# ns:%d\n", tab, ntohs(pd->dns.nscount));
printf("%s# ar:%d\n", tab, ntohs(pd->dns.arcount));


printf("RESOURCE RECORDS\n");
int numRRs = ntohs(pd->dns.qdcount) + ntohs(pd->dns.ancount) + ntohs(pd->dns.nscount) + ntohs(pd->dns.arcount);
int i;
if (ntohs(pd->udp.sport) == 53)
{
//numRRs = 0;   
for(i=0; i<numRRs; i++){
    printf("SizeofURL:(%d)", sizeofUrl(pd->data)-2); print_url(pd->data); printf("\n");
    // extract variables
    static_RR* RRd = (static_RR*)((void*)pd->data + sizeofUrl(pd->data));
    int type = ntohs(RRd->type);
    if (type == 1)
    {
        int ttl = (uint32_t)ntohl(RRd->ttl);
        printf("%sTTL:%d \n", tab, ttl);
    }
}

The output off the above code looks like this:

IP HEADER
   source:192.168.1.1
   dest:192.168.1.7
UDP HEADER
   source port:53
   dest port:64740
DNS HEADER
   id:44005
   flags:33152
   # questions:1
   # answers:1
   # ns:0
   # ar:0
RESOURCE RECORDS
SizeofURL:(16).www.google.co.nz
   TTL:-1072955391 
SizeofURL:(16).www.google.co.nz
   TTL:-1072955391 

any idea what's wrong with the code? Is using "ns_parserr" the best way to go?

Answer 1

I'm no expert but mine works. Make sure you have it defined uint32_t ttl;

and print...

printf("answer time <%d> \n", ntohs(answer->ttl));