Obtaining MAC address in C program

Question

Hello there,
I wish to obtain the MAC address of the primary ethernet card on a Solaris OS via C. This program is invoked many times/second so calling an external program is not really suitable.
The MAC address is being obtained for the purpose of providing a low-level software lock/key system (low level meaning I am aware it's relatively trivial to circumvent).
Paul.

Answer 1

Hello again.
I found out that the SIOCGARP ioctl will get the ARP entry of a certain IP address in the ethernet. Root access is not required.
The following program will print the ethernet MAC addresses of all IP networks (including dial-up and 127.0.0.1).
For Dial-up and 127.0.0.1 "No ethernet address" will be reported. If you have multiple network cards it may be a problem to find out the MAC address of the main board.
On my Blade-1000 the following output is produced:
lo0: 127.0.0.1 - No ethernet address.
eri0: 192.168.178.18 - 08:00:20:FB:2F:78Here is the program:
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <netinet/in.h>
#include <arpa/inet.h>
main(int argc,char *argv)
    unsigned char eth_addr[6];
    int i,j,sock;
    unsigned char *p;
    struct lifconf lic;
    struct lifreq lifrs[30];
    struct lifnum num;
    struct arpreq ar;
    struct sockaddr_in *soap,*soap2;
    /* Enumerate all IP addresses of the system */
    sock=socket(PF_INET,SOCK_DGRAM,IPPROTO_IP);
    num.lifn_family=AF_INET;
    num.lifn_flags=0;
    ioctl(sock,SIOCGLIFNUM,&num);
    lic.lifc_family=AF_INET;
    lic.lifc_flags=0;
    lic.lifc_len=sizeof(lifrs);
    lic.lifc_buf=(caddr_t)&(lifrs[0] );
    ioctl(sock,SIOCGLIFCONF,&lic);
    /* Get the ethernet address for each of them */
    for(i=0;i<num.lifn_count;i++)
        /* Get IP address */
        ioctl(sock,SIOCGLIFADDR,&(lifrs[ i ]));
        soap=(struct sockaddr_in *)&(lifrs[ i ].lifr_addr);
        soap2=(struct sockaddr_in *)&(ar.arp_pa);
        *soap2=*soap;
        /* Print IP address */
        p=(unsigned char *)&(soap->sin_addr);
        printf("%s: %u.%u.%u.%u - ",lifrs[ i ].lifr_name,
            p[0],p[1],p[2],p[3]);
        /* Get ethernet address */
        if(ioctl(sock,SIOCGARP,&ar)<0)
            printf("No ethernet address.\n");
        else
            p=(unsigned char *)&(ar.arp_ha.sa_data);
            printf("%02X:%02X:%02X:%02X:%02X:%02X\n",
                p[0],p[1],p[2],p[3],p[4],p[5]);
    close(sock);
}Martin