ldev.c

/* ldev.c
   
   compile with:
   >gcc ldev.c -lpcap

   looks for an interface, and lists the network ip
   and mask associated with that interface
*/
#include <stdio.h>
#include <stdlib.h>
#include <pcap.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
    char *dev; /* name of the device to use */
    char *net; /* dot notation of the network address */
    char *mask;/* dot notation of the network mask    */
    int ret;   /* return code */
    char errbuf[PCAP_ERRBUF_SIZE];
    bpf_u_int32 netp; /* ip           */
    bpf_u_int32 maskp;/* subnet mask */
    struct in_addr addr;

    /* ask pcap to find a valid device for use to sniff on */
    dev = pcap_lookupdev(errbuf);

    /* error checking */
    if(dev == NULL)
    {
     printf("%s\n",errbuf);
     exit(1);
    }

    /* print out device name */
    printf("DEV: %s\n",dev);

    /* ask pcap for the network address and mask of the device */
    ret = pcap_lookupnet(dev,&netp,&maskp,errbuf);

    if(ret == -1)
    {
     printf("%s\n",errbuf);
     exit(1);
    }

    /* get the network address in a human readable form */
    addr.s_addr = netp;
    net = inet_ntoa(addr);
    
    if(net == NULL)
    {
     perror("inet_ntoa");
     exit(1);
    }

    printf("NET: %s\n",net);
    
    /* do the same as above the device's mask */
    addr.s_addr = maskp;
    mask = inet_ntoa(addr);

    if(mask == NULL)
    {
     perror("inet_ntoa");
     exit(1);
    }
  
    printf("MASK: %s\n",mask);

    return 0;
  }