Finding original MAC address from Hardware itself

Question

Os:REDHAT LINUX Linux manage: 2.6.18.8-1 #

Is this possible to read MAC address form NIC directly ? I have below code but it just read from above layer but not the card itself !!!

I'm trying to figure out how to find the original MAC address of an ethernet NIC on my linux box. I understand how to find the current MAC address using ifconfig, but if the address has been changed, say by using 'ifconfig eth0 hw ether uu:vv:ww:yy:xx:zz',or I set "permanent" it using vi /etc/sysconfig/network-scripts/ifcfg-eth0.this file...I can successfully UP it in REBOOT also. how do I find the original? There must be a way to find it, because it is still burned permanently into the card, but I can't find a tool to read the burned in address. is there any utility for it or command for it? I suppose to write C code for it. but don't know how to do this in above case.

** below code gives my current MAC but not original MAC

#include <stdio.h>              /* Standard I/O */
#include <stdlib.h>             /* Standard Library */
#include <errno.h>              /* Error number and related */


#define ENUMS
#include <sys/socket.h>
#include <net/route.h>
#include <net/if.h>
#include <features.h>           /* for the glibc version number */
#if __GLIBC__ >= 2 && __GLIBC_MINOR >= 1
#include <netpacket/packet.h>
#include <net/ethernet.h>       /* the L2 protocols */
#else
#include <asm/types.h>
#include <linux/if_packet.h>
#include <linux/if_ether.h>     /* The L2 protocols */
#endif
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <sys/ioctl.h>
#include <netdb.h>


int main( int argc, char * argv[] ){

unsigned char  mac[IFHWADDRLEN];
int i;
    get_local_hwaddr( argv[1], mac );
    for( i = 0; i < IFHWADDRLEN; i++ ){
        printf( "%02X:", (unsigned int)(mac[i]) );
    }

}


int get_local_hwaddr(const char *ifname, unsigned char *mac)
{
    struct ifreq ifr;
    int fd;
    int rv;                     // return value - error value from df or ioctl call

    /* determine the local MAC address */
    strcpy(ifr.ifr_name, ifname);
    fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
    if (fd < 0)
        rv = fd;
    else {
        rv = ioctl(fd, SIOCGIFHWADDR, &ifr);
        if (rv >= 0)            /* worked okay */
            memcpy(mac, ifr.ifr_hwaddr.sa_data, IFHWADDRLEN);
    }

    return rv;
}

Answer 1

Certainly in ethtool 3.1 you can just print the address: ethtool -P|--show-permaddr DEVNAME Show permanent hardware address

e.g.

ethtool -P eth0

Permanent address: 94:de:80:6a:21:25