Richard Schiks Richard Schiks - 4 months ago 26
iOS Question

Getting ARP table on iPhone/iPad

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.


After importing <netinet/if_ether.h>, you should edit it and change the line

#include <net/if_arp.h>


#include "if_arp.h"

and then import <net/if_arp.h> 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. You can find above files from following links: Files under "netinet" Files under "net"