IP Helper Functions

The IP Helper API provides a set of functions that enable applications to retrieve and modify network configuration settings. Below is a list of the most commonly used functions.

Function	Header	Description	Sample
`GetAdaptersInfo`	`iphlpapi.h`	Retrieves adapter information for the local computer.	View
`GetIfTable`	`iphlpapi.h`	Retrieves a table of interface entries.	View
`GetIpForwardTable`	`iphlpapi.h`	Retrieves the IP routing table.	View
`FlushIpNetTable`	`iphlpapi.h`	Deletes all entries from the ARP table.	View
`SetDHCPOptionInfo`	`iphlpapi.h`	Configures DHCP options for a specific scope.	View

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

#pragma comment(lib, "iphlpapi.lib")

int main() {
    DWORD dwSize = 0;
    GetAdaptersInfo(NULL, &dwSize);
    PIP_ADAPTER_INFO pAdapterInfo = (PIP_ADAPTER_INFO)malloc(dwSize);
    if (GetAdaptersInfo(pAdapterInfo, &dwSize) == NO_ERROR) {
        PIP_ADAPTER_INFO pAdapter = pAdapterInfo;
        while (pAdapter) {
            printf("Adapter: %s\n", pAdapter->Description);
            printf("IP Address: %s\n", pAdapter->IpAddressList.IpAddress.String);
            pAdapter = pAdapter->Next;
        }
    }
    free(pAdapterInfo);
    return 0;
}

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

#pragma comment(lib, "iphlpapi.lib")

int main() {
    MIB_IFTABLE *pIfTable = NULL;
    DWORD dwSize = 0;
    GetIfTable(NULL, &dwSize, FALSE);
    pIfTable = (MIB_IFTABLE *)malloc(dwSize);
    if (GetIfTable(pIfTable, &dwSize, FALSE) == NO_ERROR) {
        for (DWORD i = 0; i < pIfTable->dwNumEntries; i++) {
            MIB_IFROW *row = &pIfTable->table[i];
            wprintf(L"Interface %d: %s (%u)\n",
                i, row->wszName, row->dwOperStatus);
        }
    }
    free(pIfTable);
    return 0;
}

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

#pragma comment(lib, "iphlpapi.lib")

int main() {
    PMIB_IPFORWARDTABLE pTable = NULL;
    DWORD dwSize = 0;
    GetIpForwardTable(NULL, &dwSize, FALSE);
    pTable = (PMIB_IPFORWARDTABLE)malloc(dwSize);
    if (GetIpForwardTable(pTable, &dwSize, FALSE) == NO_ERROR) {
        for (DWORD i = 0; i < pTable->dwNumEntries; i++) {
            MIB_IPFORWARDROW *row = &pTable->table[i];
            printf("Dest: %s  Mask: %s  NextHop: %s\n",
                inet_ntoa(*(struct in_addr *)&row->dwForwardDest),
                inet_ntoa(*(struct in_addr *)&row->dwForwardMask),
                inet_ntoa(*(struct in_addr *)&row->dwForwardNextHop));
        }
    }
    free(pTable);
    return 0;
}

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

#pragma comment(lib, "iphlpapi.lib")

int main() {
    DWORD dwResult = FlushIpNetTable2(NULL);
    if (dwResult == NO_ERROR) {
        printf("ARP table flushed successfully.\n");
    } else {
        printf("Failed to flush ARP table. Error: %lu\n", dwResult);
    }
    return 0;
}

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

#pragma comment(lib, "dhcpsapi.lib")

int main() {
    DHCP_OPTION_DATA optionData = {0};
    DHCP_OPTION_VALUE optionValue = {0};
    optionValue.OptionID = OPTION_ROUTER_ADDRESS;
    optionValue.ValueType = DHCP_BINARY_DATA;
    optionValue.Value.BinaryData.Data = (BYTE *)malloc(4);
    optionValue.Value.BinaryData.Len = 4;
    // Set router IP to 192.168.1.1
    optionValue.Value.BinaryData.Data[0] = 192;
    optionValue.Value.BinaryData.Data[1] = 168;
    optionValue.Value.BinaryData.Data[2] = 1;
    optionValue.Value.BinaryData.Data[3] = 1;
    optionData.OptionValue = &optionValue;
    optionData.NumElements = 1;

    DWORD dwRet = DhcpSetOptionInfoV5(
        NULL,          // Server IP (NULL = local)
        L"Scope1",     // Scope name
        &optionData,
        DHCP_OPTION_ROUTER_ADDRESS
    );

    if (dwRet == ERROR_SUCCESS) {
        wprintf(L"Router option set successfully.\n");
    } else {
        wprintf(L"Failed to set router option. Error: %lu\n", dwRet);
    }

    free(optionValue.Value.BinaryData.Data);
    return 0;
}