getting arp table on iphone ipad

getting arp table on iphone ipad  using -'objective-c,ios,xcode,arp'

I am trying to get the ARP entries on my iPad like here.

When compiling the code to run on my iPad (so not the simulator) I am getting missing header error messages. You can resolve them by copying the header files into you project locally as mentioned in this post.

The problem lies in the line

  sdl = (struct sockaddr_dl *)(sin + 1);

in this piece of code:

-(NSString*) ip2mac: (char*) ip

    int expire_time, flags, export_only, doing_proxy, found_entry;

    NSString *mAddr = nil;
    u_long addr = inet_addr(ip);
    int mib[6];
    size_t needed;
    char *host, *lim, *buf, *next;
    struct rt_msghdr *rtm;
    struct sockaddr_inarp *sin;
    struct sockaddr_dl *sdl;
    extern int h_errno;
    struct hostent *hp;

    mib[0] = CTL_NET;
    mib[1] = PF_ROUTE;
    mib[2] = 0;
    mib[3] = AF_INET;
    mib[4] = NET_RT_FLAGS;
    mib[5] = RTF_LLINFO;
    if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
        err(1, "route-sysctl-estimate");
    if ((buf = malloc(needed)) == NULL)
        err(1, "malloc");
    if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0)
        err(1, "actual retrieval of routing table");

    lim = buf + needed;
    for (next = buf; next < lim; next += rtm->rtm_msglen) {
        rtm = (struct rt_msghdr *)next;
        sin = (struct sockaddr_inarp *)(rtm + 1);
        sdl = (struct sockaddr_dl *)(sin + 1);
        if (addr) {
            if (addr != sin->sin_addr.s_addr)
            found_entry = 1;
        if (nflag == 0)
            hp = gethostbyaddr((caddr_t)&(sin->sin_addr),
                               sizeof sin->sin_addr, AF_INET);
            hp = 0;
        if (hp)
            host = hp->h_name;
        else {
            host = "?";
            if (h_errno == TRY_AGAIN)
                nflag = 1;

        if (sdl->sdl_alen) {

            u_char *cp = LLADDR(sdl);

            mAddr = [NSString stringWithFormat:@"%x:%x:%x:%x:%x:%x", cp[0], cp[1], cp[2], cp[3], cp[4], cp[5]];

        //  ether_print((u_char *)LLADDR(sdl));

            mAddr = nil;


    if (found_entry == 0) {
        return nil;
    } else {
        return mAddr;


It gives the following error message:

Arithmetic on pointer to incomplete type 'struct sockaddr_inarp*'

When you compile the code for the iPad simulator everything runs fine.

Does anyone have an idea how to solve this?
A similar question (but not solved) is asked here.

asked Sep 15, 2015 by RolandoAnnun
0 votes

2 Answers

0 votes

After importing , you should edit it and change the line



#include "if_arp.h"

and then import in your project as well. This should fix that error.

Anyway the headers you need to import to compile the code you posted are:

#include "if_ether.h"
#include "route.h"
#include "if_arp.h"
#include "if_dl.h"

Hope this helps =)


You need to "Add files to project", not simply importing it with #import or #include.

answered Sep 15, 2015 by IolSparling
0 votes

instead of messing with the original headers. More info here: Implicit declaration of function 'ether_ntoa' is invalid in C99

answered Sep 15, 2015 by KaseyLeoneas