This sample illustrates how to programmatically change an IP address for a specific network adapter on your machine. This program also demonstrates how to retrieve existing network adapter IP configuration information using Win32 APIs.

IP configurations can be changed for a specific network adapter by using the AddIpAddress() and DeleteIpAddress() Ip Helper API functions. These functions require you to understand adapter index numbers and IP context numbers. In Windows, every network adapter has a unique index ID and every IP address has a unique context ID. Adapter index IDs and IP context numbers can be retrieved using the GetAdaptersInfo() IP Helper function. This program features a list option that displays current network adapter configuration information by showing all adapters index numbers and IP address context numbers associated with their corresponding network adaptors.

To execute this application, simply build the application using the Visual C++ (Version 5 SP 3 or better) Nmake.exe program generation facility. An ipchange.exe program should result. Execute the ipchange.exe with the following parameters:

Ipchange.exe [ -l ] [ -a -n -i -m ] [ -d -c]

  1. -l List adapter index IDs and IP Address context ID information
  2. -a Add IP Address option
  3. -d Delete IP Address option
  4. -i IP Address to specify with -a option
  5. -m Subnet Mask to specify with -a option
  6. -c IP context ID for an existing IP address -n Index ID of an existing network
    adapter

Author: Jim Ohlund 21-Apr-98

#include <winsock2.h>
#include <windows.h>
#include <stdio.h>

void Usage(void) {
    printf("Usage: Ipchange [ -l ] [ -a -n -i -m ] "
        "[ -d -c]\n\n"
        "\t -l List adapter index IDs and IP Address context ID information\n"
        "\t -a Add IP Address option\n"
        "\t -d Delete IP Address option\n"
        "\t -i IP Address to specify with -a option\n"
        "\t -m Subnet Mask to specify with -a option\n"
        "\t -c IP context ID for an existing IP address\n"
        "\t -n Index ID of an existing network adapter\n");
}

void main(int argc, char* argv[]) {
    ULONG NTEContext = 0;
    ULONG NTEInstance;
    IPAddr NewIP;
    IPAddr NewMask;
    DWORD Index;
    DWORD Context;
    CHAR NewIPStr[64];
    CHAR NewMaskStr[64];

    PIP_ADAPTER_INFO pAdapterInfo, pAdapt;
    PIP_ADDR_STRING pAddrStr;
    DWORD AdapterInfoSize;
    DWORD Err;
    BOOL OptList = FALSE;
    BOOL OptAdd = FALSE;
    BOOL OptDel = FALSE;

    NewIPStr[0] = '\0';
    NewMaskStr[0] = '\0';
    Context = Index = -1;
    for (int i = 1; i < argc; i++) {
        if ((argv[i][0] == '-') || (argv[i][0] == '/')) {
            switch (tolower(argv[i][1])) {
            case 'l':
                OptList = TRUE;
                break;
            case 'a':
                OptAdd = TRUE;
                break;
            case 'c':
                if (strlen(argv[i]) > 2)
                    Context = atoi(&argv[i][2]);
                break;
            case 'd':
                OptDel = TRUE;
                break;
            case 'i':
                if (strlen(argv[i]) > 2)
                    strcpy(NewIPStr, &argv[i][2]);
                break;
            case 'm':
                if (strlen(argv[i]) > 2)
                    strcpy(NewMaskStr, &argv[i][2]);
                break;
            case 'n':
                if (strlen(argv[i]) > 2)
                    Index = atoi(&argv[i][2]);
                break;
            default:
                printf("default\n");
                Usage();
                return;
            }
        }
        else {
            printf("else\n");
            Usage();
            return;
        }
    }

    // Check options
    if ((OptAdd && (Index == -1 || NewIPStr[0] == '\0' || NewMaskStr[0] == '\0')) ||
        (OptDel && Context == -1)) {
        Usage();
        return;
    }

    // Get sizing information about all adapters
    AdapterInfoSize = 0;
    if ((Err = GetAdaptersInfo(NULL, &AdapterInfoSize)) != 0) {
        if (Err != ERROR_BUFFER_OVERFLOW) {
            printf("GetAdaptersInfo sizing failed with error %d\n", Err);
            return;
        }
    }

    // Allocate memory from sizing information
    if ((pAdapterInfo = (PIP_ADAPTER_INFO)GlobalAlloc(GPTR, AdapterInfoSize)) == NULL) {
        printf("Memory allocation error\n");
        return;
    }

    // Get actual adapter information
    if ((Err = GetAdaptersInfo(pAdapterInfo, &AdapterInfoSize)) != 0) {
        printf("GetAdaptersInfo failed with error %d\n", Err);
        return;
    }

    if (OptList) {
        printf("MAC Address - Adapter\n"
            "Index     Context   Ip Address          Subnet Mask\n"
            "--------------------------------------------------------------\n");

        pAdapt = pAdapterInfo;

        while (pAdapt) {
            for (UINT i = 0; iAddressLength; i++) {
                if (i == (pAdapt->AddressLength - 1))
                    printf("%.2X - ", (int)pAdapt->Address[i]);
                else
                    printf("%.2X-", (int)pAdapt->Address[i]);
            }
            printf("%s\n", pAdapt->Description);

            pAddrStr = &(pAdapt->IpAddressList);
            while (pAddrStr) {
                printf("%-10.d%-10.d%-20.20s%s\n", 
                    pAdapt->Index, pAddrStr->Context, 
                    pAddrStr->IpAddress.String, pAddrStr->IpMask.String);
                pAddrStr = pAddrStr->Next;
            }

            pAdapt = pAdapt->Next;
        }
    }

    if (OptAdd) {
        NewIP = inet_addr(NewIPStr);
        NewMask = inet_addr(NewMaskStr);
        if ((Err = AddIPAddress(NewIP, NewMask, Index, 
&NTEContext, &NTEInstance)) != 0) {
            printf("AddIPAddress failed with error %d, %d\n", NTEContext, Err);
            return;
        }
    }

    if (OptDel) {
        if ((Err = DeleteIPAddress(Context)) != 0)
            printf("DeleteIPAddress failed %d\n", Err);
    }
}