What exactly means iOS networking interface name?

Question

I use following code to print all interface and it's mac address

- ( void )interfaceInfo{

int                 mib[6];
size_t              len;
char                *buf;
unsigned char       *ptr;
struct if_msghdr    *ifm;
struct sockaddr_dl  *sdl;

mib[0] = CTL_NET;
mib[1] = AF_ROUTE;
mib[2] = 0;
mib[3] = AF_LINK;
mib[4] = NET_RT_IFLIST;

char name[128];
memset(name, 0, sizeof(name));
for (int i=1; i<20; i ++) {
    if (if_indextoname(i, name)) {
        printf("%s ",name);            
    }else{
        continue;
    }

    if ((mib[5] = if_nametoindex(name)) == 0) {
        printf("Error: if_nametoindex error\n");
        return NULL;
    }

    if (sysctl(mib, 6, NULL, &len, NULL, 0) < 0) {
        printf("Error: sysctl, take 1\n");
        return NULL;
    }

    if ((buf = malloc(len)) == NULL) {
        printf("Could not allocate memory. error!\n");
        return NULL;
    }

    if (sysctl(mib, 6, buf, &len, NULL, 0) < 0) {
        printf("Error: sysctl, take 2");
        free(buf);
        return NULL;
    }

        ifm = (struct if_msghdr *)buf;
        sdl = (struct sockaddr_dl *)(ifm + 1);
        ptr = (unsigned char *)LLADDR(sdl);
        NSString *macString = [NSString stringWithFormat:@"%02X:%02X:%02X:%02X:%02X:%02X",
                       *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5)];
        printf(" %s\n",[macString cStringUsingEncoding:NSUTF8StringEncoding]);
        free(buf);
    }
    return nil;
}

I run the code on iPhone 5 and the output is

lo0  00:00:00:00:00:00
pdp_ip0  00:00:00:00:00:00
pdp_ip1  00:00:00:00:00:00
pdp_ip2  00:00:00:00:00:00
pdp_ip3  00:00:00:00:00:00
ap1  EA:8D:28:44:32:2F
en0  E8:8D:28:44:32:2F
en1  EA:8D:28:44:32:31
awdl0  4A:79:85:44:5B:4D
//I faked parts data

I wanna know what's the pdp_ip? and what's the ap1,en1?

I find out en0 is wifi hardware mac address

Does ap1 and en1 is virtual interface?

Thank you!

Answer 1

lo = localhost
en = ethernet
ap = Probably for access point (if you are acting as a wifi host)

pdp_ip = maybe PDS data packet? PDS is the Phone Data Service, the data portion of GSM. Since there are four, I might postulate that PDS has the capability to offer four discrete channels.

Answer 2

Note this code appears to be copy-pasted from Getting Device ID or Mac Address in iOS with the helpful comments removed. You might want to look at that discussion instead.

Answer 3

From my research it appears (i.e. I haven't found any confirming documentation) that if the code above returns more than one "awdl0" entry then Wi-Fi is enabled. Similarly, more than one "pdp_ip0" entry indicates that cellular data is enabled. Other libraries (most notably Reachability) can then be used to indicate that a data connection has been made using either of the above.

Answer 4

ap1, en0, en1 are names of the interfaces on iOS as well as on Mac. If you type in Terminal on Mac ifconfig you would get the same, en0, en1, etc.

pdp_ip interfaces are those that are used for 3G and cellular data, while ap1 is used to represent currently active data connection, Wi-Fi, cellular data or bluetooth.