Windows API Reference

IP Helper API (IPHlpAPI)

The IP Helper API (IPHlpAPI) is a set of functions that provide access to information about the TCP/IP protocol stack and network adapters on a local computer. This API allows you to retrieve and modify network configuration settings, manage routing tables, and obtain information about network interfaces, IP addresses, ARP caches, and more.

Key Functionality

• Retrieving information about network adapters (e.g., name, description, MAC address).
• Getting and setting IP addresses, subnet masks, and default gateways.
• Managing the ARP cache.
• Accessing and modifying the routing table.
• Obtaining information about TCP and UDP connections.
• Monitoring network statistics.

Core Concepts

Understanding the following concepts is crucial when working with the IP Helper API:

• Network Adapters: Physical or virtual network interfaces on the system.
• IP Addresses: Logical addresses assigned to network interfaces.
• Subnet Masks: Used to divide an IP address into network and host portions.
• Default Gateway: The router used to forward packets to other networks.
• ARP Cache: Stores mappings between IP addresses and MAC addresses.
• Routing Table: Contains information about how to route network traffic.

Common Use Cases

• Developing network diagnostic tools.
• Implementing custom network monitoring solutions.
• Automating network configuration tasks.
• Gathering network performance data.

Key Functions and Structures

The following are some of the most frequently used functions and data structures within the IP Helper API:

Functions

• GetAdaptersInfo: Retrieves adapter configuration information.
• GetIpAddrTable: Retrieves the IP address table.
• GetRouteTable: Retrieves the routing table entries.
• GetTcpTable: Retrieves the TCP connection table.
• GetUdpTable: Retrieves the UDP listener table.
• SendARP: Sends an ARP request.

Structures

• IP_ADAPTER_INFO: Contains information about a network adapter.
• MIB_IPADDRROW: Represents an entry in the IP address table.
• MIB_IPFORWARDROW: Represents an entry in the routing table.
• MIB_TCPROW: Represents a TCP connection entry.

Getting Started with IPHlpAPI

To use the IP Helper API, you typically need to include the iphlpapi.h header file and link against the iphlpapi.lib library.

Example: Retrieving Adapter Information

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

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

int main() {
    IP_ADAPTER_INFO* pAdapterInfo;
    ULONG ulOutBufLen = sizeof(IP_ADAPTER_INFO);

    // Allocate memory for the adapter information
    pAdapterInfo = (IP_ADAPTER_INFO*)malloc(sizeof(IP_ADAPTER_INFO));

    if (pAdapterInfo == NULL) {
        printf("Error allocating memory\n");
        return 1;
    }

    // Call GetAdaptersInfo to get adapter information
    if (GetAdaptersInfo(pAdapterInfo, &ulOutBufLen) == ERROR_BUFFER_OVERFLOW) {
        // Buffer was too small, reallocate
        free(pAdapterInfo);
        pAdapterInfo = (IP_ADAPTER_INFO*)malloc(ulOutBufLen);
        if (pAdapterInfo == NULL) {
            printf("Error allocating memory for expanded buffer\n");
            return 1;
        }
    }

    if (GetAdaptersInfo(pAdapterInfo, &ulOutBufLen) == NO_ERROR) {
        IP_ADAPTER_INFO* pAdapter = pAdapterInfo;
        while (pAdapter) {
            printf("Adapter Name: %s\n", pAdapter->AdapterName);
            printf("  Description: %s\n", pAdapter->Description);
            printf("  MAC Address: %02X-%02X-%02X-%02X-%02X-%02X\n",
                   pAdapter->Address[0], pAdapter->Address[1], pAdapter->Address[2],
                   pAdapter->Address[3], pAdapter->Address[4], pAdapter->Address[5]);
            printf("  IP Address: %s\n", pAdapter->IpAddressList.IpAddress.String);
            printf("  Subnet Mask: %s\n", pAdapter->IpAddressList.SubnetMask.String);
            printf("  Default Gateway: %s\n", pAdapter->GatewayList.IpAddress.String);
            printf("\n");
            pAdapter = pAdapter->Next;
        }
    } else {
        printf("Error calling GetAdaptersInfo\n");
    }

    // Free allocated memory
    if (pAdapterInfo) {
        free(pAdapterInfo);
    }

    return 0;
}