From owner-freebsd-hackers  Wed Jun 19  8:54: 1 2002
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Date: Wed, 19 Jun 2002 09:53:27 -0600
From: John E Hein <jhein@timing.com>
To: kevin@wooten.com
Cc: hackers@FreeBSD.ORG
Subject: Retrieving interface MAC address
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"Kevin D. Wooten" <kevin@wooten.com> wrote at 13:41:02 -0700 on 18 Jun 2002:
 > Thanks getifaddrs() works great, just one more thing is there a simple 
 > way to tell the difference between "real" interfaces and virtual ones? I 
 > could obviously exclude the easy ones ( i.e. lo, lp, faith, ... ) by 
 > looking at the name, but I am not sure how many different virtual 
 > interfaces there are ( or will be ).

This gets link interfaces and further checks for just ethernet types:

get_if_name(char if_name[IFNAMSIZ])
{
    struct ifaddrs   *ifaphead;

    if (getifaddrs(&ifaphead) != 0)
        perror("get_if_name: getifaddr() failed");
    else
    {
        bool              found = false;
        struct ifaddrs   *ifap;

        for (ifap = ifaphead; ifap && !found; ifap = ifap->ifa_next)
        {
            if ((ifap->ifa_addr->sa_family == AF_LINK)
                && (((struct sockaddr_dl *) ifap->ifa_addr)->sdl_type ==
                    IFT_ETHER))
            {
                found = true;
                strlcpy(if_name, ifap->ifa_name, IFNAMSIZ);
                printf("found ethernet if: %s\n", if_name);
            }
        }
        if (!found)
        {
            fprintf(stderr, "get_if_name: did not find ethernet if\n");
            strlcpy(if_name, "", IFNAMSIZ);
        }
    }
}

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