C - Determine network and netmask address using pcap
====================================================

Public domain
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    /* gcc -lpcap pcap_lookupnet.c */
    #include   <pcap.h>
    #include   <arpa/inet.h>
    #include   <stdlib.h>
     
    int main()
    {
            char errbuf[PCAP_ERRBUF_SIZE];
            char dev[]="eth0";
            char *net_quad;
            char *mask_quad;
            bpf_u_int32 net_bin;
            bpf_u_int32 mask_bin;
            struct in_addr addr;
     
            printf("IF: %s\n", dev);
     
            /* ask pcap to determine the IPv4 network number
             * and mask associated with the network device
             * in binary format
             */
            if(pcap_lookupnet(dev,&net_bin,&mask_bin,errbuf) == -1 ) {
                    printf("%s\n",errbuf);
                    exit(EXIT_FAILURE);
            }
     
            /* Convert binary net to quad-dotted-decimal */
            addr.s_addr = net_bin;
            if ((net_quad=inet_ntoa(addr)) == NULL) {
                    perror("inet_ntoa");
                    exit(EXIT_FAILURE);
            }
            printf("NET: %s\n", net_quad);
     
            /* Convert binary mask to quad-dotted-decimal */
            addr.s_addr = mask_bin;
            if ((mask_quad=inet_ntoa(addr)) == NULL) {
                    perror("inet_ntoa");
                    exit(EXIT_FAILURE);
            }
            printf("MASK: %s\n", net_quad);
     
            exit(EXIT_SUCCESS);
    }

********************************************************************************
_BY: Pejman Moghadam_  
_TAG: c, pcap_  
_DATE: 2011-02-23 17:08:00_