how to find the MAC address of another computer (client server)? - mfc

Question

i am trying to get the MAC address of another computer using a server and client program in c++ using UDP connections. The server is on one computer (it contains 2 listboxes, 1 for the IP addresses of connected clients, the other for the MAC address) the client is on another computer. my current code only gets the MAC address if i run the server and client and the same computer. When i debug the program i see that when trying to get the MAC address of another computer the program doesn't go into the if statement and run the line PrintMACaddress(pAdapterInfo->Address);
void CmfcServerDlg:: PrintMACFromIP(const CString &selected_ip_adr)
{
IP_ADAPTER_INFO AdapterInfo[16];
DWORD dwBufLen = sizeof(AdapterInfo);
DWORD dwStatus = GetAdaptersInfo(
AdapterInfo,
&dwBufLen);
assert(dwStatus == ERROR_SUCCESS);
PIP_ADAPTER_INFO pAdapterInfo = AdapterInfo;// Contains pointer to current adapter info
bool found = false;
do {
const IP_ADDR_STRING *addr_str = &pAdapterInfo->IpAddressList;
if (addr_str != NULL)
{
if (selected_ip_adr == addr_str->IpAddress.String)
{
PrintMACaddress(pAdapterInfo->Address);
}
}
pAdapterInfo = pAdapterInfo->Next;
}
while(pAdapterInfo);
}
i found that using the ARP function may help with this or since the MAC address is data i may transmit it as a string or raw data but i have idea how to this
here is the PrintMAC function:
void CmfcServerDlg::PrintMACaddress(unsigned char MACData[])
{
CString strText;
strText.Format("%02X-%02X-%02X-%02X-%02X-%02X\n",MACData[0], MACData[1], MACData[2], MACData[3], MACData[4], MACData[5]);
m_ClientIdList.AddString(strText);
}

Answer 1

The GetAdaptersInfo function only returns the addresses of the adapters attached to the local computer. You should take a look to SendARP.
EDIT: Try this:
void CmfcServerDlg::PrintMACFromIP(const CString &selected_ip_adr)
{
DWORD dwRetVal;
IPAddr DestIp = 0;
IPAddr SrcIp = 0; /* default for src ip */
ULONG MacAddr[2]; /* for 6-byte hardware addresses */
ULONG PhysAddrLen = 6; /* default to length of six bytes */
char *SrcIpString = NULL;
BYTE *bPhysAddr;
DestIp = inet_addr(CT2A(selected_ip_adr));
memset(&MacAddr, 0xff, sizeof (MacAddr));
dwRetVal = SendARP(DestIp, SrcIp, &MacAddr, &PhysAddrLen);
if (dwRetVal == NO_ERROR) {
bPhysAddr = (BYTE *) & MacAddr;
if (PhysAddrLen) {
CString theMac;
theMac.Format(_T("%.2X-%.2X-%.2X-%.2X-%.2X-%.2X"), (int) bPhysAddr[0],
(int) bPhysAddr[1],(int) bPhysAddr[2],(int) bPhysAddr[3],(int) bPhysAddr[4],
(int) bPhysAddr[5]);
PrintMACaddress(theMac);
} else
printf
("Warning: SendArp completed successfully, but returned length=0\n");
} else {
printf("Error: SendArp failed with error: %d", dwRetVal);
switch (dwRetVal) {
case ERROR_GEN_FAILURE:
printf(" (ERROR_GEN_FAILURE)\n");
break;
case ERROR_INVALID_PARAMETER:
printf(" (ERROR_INVALID_PARAMETER)\n");
break;
case ERROR_INVALID_USER_BUFFER:
printf(" (ERROR_INVALID_USER_BUFFER)\n");
break;
case ERROR_BAD_NET_NAME:
printf(" (ERROR_GEN_FAILURE)\n");
break;
case ERROR_BUFFER_OVERFLOW:
printf(" (ERROR_BUFFER_OVERFLOW)\n");
break;
case ERROR_NOT_FOUND:
printf(" (ERROR_NOT_FOUND)\n");
break;
default:
printf("\n");
break;
}
}
}
void CmfcServerDlg::PrintMACaddress(CString& strText)
{
m_ClientIdList.AddString(strText);
}