How to get selected adapter's MAC address in WinPcap?

Question

For example, when program runs, I entered 1 as input and wanted to get MAC address of that interface in here. How can I do that?

Answer 1

I did a lot of work trying to figure out how to both get the mac address for an arbitrary interface under Windows, and matching that to the device info you get back from WinPCap.

A lot of posts say you should use GetAdaptersInfo or similar functions to get the mac address, but unfortunately, those functions only work with an interface that has ipv4 or ipv6 bound to it. I had a network card that purposely wasn't bound to anything, so that Windows wouldn't send any data over it.

GetIfTable(), however, seems to actually get you every interface on the system (there were 40 some odd on mine). It has the hardware mac address for each interface, so you just need to match it to the corresponding WinPCap device. The device name in WinPCap has a long GUID, which is also present in the name field of the interface table entries you get from GetIfTable. The names don't match exactly, though, so you have to extract the GUID from each name and match that. An additional complication is that the name field in the WinPCap device is a regular character string, but the name in the data you get from GetIfTable is a wide character string. The code below worked for me on two different systems, one Windows 7 and another Windows 10. I used the Microsoft GetIfTable example code as a starting point:

#include <winsock2.h>
#include <iphlpapi.h>
#include <stdio.h>
#include <stdlib.h>
#pragma comment(lib, "IPHLPAPI.lib")

#include <pcap.h>

// Compare the guid parts of both names and see if they match
int compare_guid(wchar_t *wszPcapName, wchar_t *wszIfName)
{
    wchar_t *pc, *ic;

    // Find first { char in device name from pcap
    for (pc = wszPcapName; ; ++pc)
    {
        if (!*pc)
            return -1;

        if (*pc == L'{'){
            pc++;
            break;
        }
    }

    // Find first { char in interface name from windows
    for (ic = wszIfName; ; ++ic)
    {
        if (!*ic)
            return 1;

        if (*ic == L'{'){
            ic++;
            break;
        }
    }

    // See if the rest of the GUID string matches
    for (;; ++pc,++ic)
    {
        if (!pc)
            return -1;

        if (!ic)
            return 1;

        if ((*pc == L'}') && (*ic == L'}'))
            return 0;

        if (*pc != *ic)
            return *ic - *pc;
    }
}

// Find mac address using GetIFTable, since the GetAdaptersAddresses etc     functions
// ony work with adapters that have an IP address
int get_mac_address(pcap_if_t *d, u_char mac_addr[6])
{
    // Declare and initialize variables.

    wchar_t* wszWideName = NULL;

    DWORD dwSize = 0;
    DWORD dwRetVal = 0;

    int nRVal = 0;

    unsigned int i;


    /* variables used for GetIfTable and GetIfEntry */
    MIB_IFTABLE *pIfTable;
    MIB_IFROW *pIfRow;

    // Allocate memory for our pointers.
    pIfTable = (MIB_IFTABLE *)malloc(sizeof(MIB_IFTABLE));
    if (pIfTable == NULL) {
        return 0;
    }
    // Make an initial call to GetIfTable to get the
    // necessary size into dwSize
    dwSize = sizeof(MIB_IFTABLE);
    dwRetVal = GetIfTable(pIfTable, &dwSize, FALSE);

    if (dwRetVal == ERROR_INSUFFICIENT_BUFFER) {
        free(pIfTable);
        pIfTable = (MIB_IFTABLE *)malloc(dwSize);
        if (pIfTable == NULL) {
            return 0;
        }

        dwRetVal = GetIfTable(pIfTable, &dwSize, FALSE);
    }

    if (dwRetVal != NO_ERROR)
        goto done;

    // Convert input pcap device name to a wide string for compare
    {
        size_t stISize,stOSize;

        stISize = strlen(d->name) + 1;

        wszWideName = malloc(stISize * sizeof(wchar_t));

        if (!wszWideName)
            goto done;

        mbstowcs_s(&stOSize,wszWideName,stISize, d->name, stISize);
    }

    for (i = 0; i < pIfTable->dwNumEntries; i++) {
        pIfRow = (MIB_IFROW *)& pIfTable->table[i];

        if (!compare_guid(wszWideName, pIfRow->wszName)){
            if (pIfRow->dwPhysAddrLen != 6)
                continue;

            memcpy(mac_addr, pIfRow->bPhysAddr, 6);
            nRVal = 1;
            break;
        }
    }

done:
    if (pIfTable != NULL) 
        free(pIfTable);
    pIfTable = NULL;

    if (wszWideName != NULL)
        free(wszWideName);
    wszWideName = NULL;

    return nRVal;
}