Find DNS names given Subnet Mask and Network Address

You might not be able to.  In order to find a host name based on the IP address there needs to be a PTR record for the address setup.

What you would need to do is do a DNS query for the the host "name" d.c.b.a.in-addr.arpa  the d.c.b.a is the IP address backwards.

So if you knew the IP address was 10.23.4.15 you would look up 15.4.23.10.in-addr.arpa.

I know it's possible to complete this task using the networking API but everything about this API is highly confusing to me. Do you know of any place I can go where I can find out about unix network programming syntax? I know all hosts on a subnet have the same network address and subnet mask values.

I know how to use the subnet mask to obtain the network address from a given IP address. First, convert the subnet mask and IP address to binary and perform an AND operation on them to obtain the network address.

Given this, how can I find the IP Address given the subnet mask and network address???

To giltjr:  What do you mean when you say PTR; do you mean pointer? I'm pretty sure I don't need a dns query because what I'm doing shouldn't involve sockets.

Here's an example of how I can find the DNS given the subnet id.

Given the subnet mask and a network address in dotted-decimal notation, I'd like to find all the DNS names assigned to all hosts on that subnet.

#include <netdb.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <string.h>
#include <stddef.h>
 
int main(int argcount, char* argvector[])
{
   if(argcount <= 1)
   {
      printf("\n\nThe usage for this program is \"listDNS (target subnet id)\".\n");
      printf("\n   Example: listDNS 165.95.5.0\n\n");
      return 0;
   }
   
   struct hostent *hostPtr;
   char* ip_addr_dot;
   char ip_addr_tmp[16];
   struct in_addr *addrPtr;
   u_long ip_addr_long;
   u_long ip_addr_long_nl;
 
   //parse argument (ip address) to ip_addr_dot
   ip_addr_dot = argvector[1];
 
   //determine last octet in ip address
   strcpy(ip_addr_tmp, ip_addr_dot );
   const char delimiters[] = ".";
   char *token;
   token = strtok( ip_addr_tmp, delimiters );
   token = strtok( NULL, delimiters );
   token = strtok( NULL, delimiters );
   token = strtok( NULL, delimiters );
  
   if( token == NULL )
   {
       printf("Error: the ip address you have provided is not valid!\n"); 
       return 0;
   }
   
   //convert last octet into an integer
   int lastOctet = atoi(token);
 
   //convert ip address string into long integer
   ip_addr_long = inet_addr(ip_addr_dot);
 
   while( lastOctet < 255 )
   {
     //convert to long and increment ip address
     ip_addr_long_nl = htonl(ip_addr_long);  //outputs 0.10.95.165          
     ip_addr_long_nl++;                      //increments to 1.10.95.165     
     ip_addr_long = htonl(ip_addr_long_nl);  //converts back to 165.95.10.1  
 
     addrPtr = (struct in_addr *) &ip_addr_long;
 
     hostPtr = gethostbyaddr(addrPtr, 4, AF_INET);
     if( hostPtr != NULL )
     {
        // Display IP addresses
        while(*(hostPtr->h_addr_list) != NULL)
        {      
          addrPtr = (struct in_addr *) *hostPtr->h_addr_list;
          printf("%s", inet_ntoa(*addrPtr));
          hostPtr->h_addr_list ++;
        }
 
        // Display Hostname
        printf(": %s",  hostPtr->h_name);
 
        while(*(hostPtr->h_aliases) != NULL)
        {
          printf(", %s", *(hostPtr->h_aliases)); 
          hostPtr->h_aliases++;
        }
 
        // Display new line
        printf("\n");
 
     }
     lastOctet++;
   }
 
   return 0;
}

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Thanks! :) Here's my solution based your and my own suggestions.
[code]
/********************************************************************
* Author: Jillian
* 2. Given a subnet mask and a network address in dotted decimal
* notation, find the DNS names assigned to all hosts on that
* particular subnet. The executable of your program must accept
* the subnet mask and the network address as command line arguments.
* The program should output the IP address and the corresponding DNS
* names for all the hosts. For example, if the name of your executable
* is listIPDNS, one should be able to run it as:
*       listIPDNS 255.255.255.0 165.95.11.15
********************************************************************/
#include
#include
#include
#include
#include
#include
#include

int main(int argcount, char* argvector[])
{
   char* inputAddress;
   char* inputMask;

   u_long inputAddressLong;
   u_long inputMaskLong;
   u_long subnetStartLong;
   u_long numHosts;
   int i;
   struct in_addr* inAddress;
   unsigned long temp;
   struct hostent *hostptr;
      
   if(argcount <= 1)
   {
      printf("\n   Example: listIPDNS 255.255.255.0 165.95.11.15\n\n");
      return 0;
   }
      
   inputMask = argvector[1];
   inputAddress = argvector[2];      
   inputAddressLong = inet_addr(inputAddress);
   inputMaskLong = inet_addr(inputMask);
   numHosts = htonl(inputMaskLong);
   subnetStartLong = inputAddressLong & inputMaskLong;
      
   for(i = 0; i < 32; i++)
      numHosts = numHosts ^ (1UL << i);
      
   i = 0;
   while(i <  numHosts)
   {
      //convert to long and increment ip address
      temp = htonl(subnetStartLong);  //outputs 0.10.95.165          
      temp++;                            //increments to 1.10.95.165    
      subnetStartLong = htonl(temp);   //converts back to 165.95.10.1  

      inAddress = (struct in_addr *) &subnetStartLong;
      
      hostptr = gethostbyaddr(inAddress, 4, AF_INET);
      if( hostptr != NULL)
      {
         // display 'ip: hostname'
       printf("%s", inet_ntoa(*inAddress));
       printf(": %s",  hostptr->h_name);
       printf("\n");
      }
      i++;
   }
      
   return 0;
}


[/code]