How Linux obtains native MAC/IP addresses

Function: Query native IP/MAC address, filter out 127.0.0.1 loop-back address

For: Linux, Ubuntu 16.04 Debug Pass

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/route.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <ifaddrs.h>

void Getlocalmacip ()

{

int i;
int Sock_mac;
Char hname[128];
struct Hostent *hent;
struct IN_ADDR *paddr = 0;
struct Ifaddrs * ifaddrstruct=null;
struct Ifreq Ifr_mac;
void * TMPADDRPTR=NULL;

struct Ifreq buf[16];
struct ifconf ifc;
int interface_num;
Char nif_name[128] = {0};
Char addressbuffer[128];

unsigned char macaddr[6] = {0};
unsigned char *pfirstbyte;

//---------------------------------------------
Get device IP address, discard loopback
//---------------------------------------------
GetHostName (hname, sizeof (hname));

Hent = gethostbyname (hname);

printf ("[%s][%d] Host:%s\n", __file__, __line__, hent->h_name);

Getifaddrs (&ifaddrstruct);

while (Ifaddrstruct!=null)
{
if (ifaddrstruct->ifa_addr->sa_family==af_inet)
{
Tmpaddrptr = & (struct sockaddr_in *) ifaddrstruct->ifa_addr)->sin_addr;
Pfirstbyte = (unsigned char*) tmpaddrptr;

if (*pfirstbyte! = 127)
{
PADDR = tmpaddrptr;
Inet_ntop (Af_inet, Tmpaddrptr, Addressbuffer, 128);
printf ("[%s][%d] NIF%s address%s\n", __file__, __line__,
Ifaddrstruct->ifa_name, Addressbuffer);
//---------------------------------------------
Remember NIF name for future use
//---------------------------------------------
strcpy (Nif_name, ifaddrstruct->ifa_name);
}

}

ifaddrstruct=ifaddrstruct->ifa_next;
}


//---------------------------------------------
Get device MAC address, discard loopback
//---------------------------------------------
Sock_mac = socket (af_inet, SOCK_DGRAM, 0);

if (Sock_mac > 0)
{
Ifc.ifc_len = sizeof (BUF);
Ifc.ifc_req = BUF;
IOCTL (Sock_mac, siocgifconf, (char *) &AMP;IFC);

Interface_num = ifc.ifc_len/sizeof (struct ifreq);

while (interface_num--)
{
if (Nif_name[0] && strcmp (Nif_name, Buf[interface_num].ifr_name))
{
Continue
}

IOCTL (Sock_mac, SIOCGIFHWADDR, (char *) &buf[interface_num]);

memcpy (MACADDR, &buf[interface_num].ifr_hwaddr.sa_data[0], 6);

printf ("NIF%s", buf[interface_num].ifr_name);
printf ("Mac%02x:%02x:%02x:%02x:%02x:%02x \ n",
Macaddr[0], macaddr[1], macaddr[2], macaddr[3], macaddr[4], macaddr[5]);
}

Close (SOCK_MAC);
}
}

How Linux obtains native MAC/IP addresses