Header and Library requirement when set/get socket options at the IPPROTO_IP level

This article provides information about the Header and Library requirement when setting or getting socket options at the IPPROTO_IP level, and the setsockopt or getsockopt function fails with runtime errors.

Original product version:   Winsock
Original KB number:   257460

Summary

When setting or getting socket options at the IPPROTO_IP level in a C/C++ Winsock application that's targeted for Windows, including the correct header and library file in the program project is critical. If the header and library files aren't properly matched, setsockopt or getsockopt may fail with runtime error 10042 (WSAENOPROTOOPT). In certain cases, even if the API returns successfully, the option value that you set or get may not be what you would have expected.

To avoid this problem, observe the following guidelines:

• A program that includes Winsock.h should only link with Wsock32.lib.

• A program that includes Ws2tcpip.h may link with either Ws2_32.lib or Wsock32.lib.

  Note

  Ws2tcpip.h must be explicitly included after Winsock2.h in order to use socket options at this level.

IPPROTO_IP level socket options in Winsock.h

The IPPROTO_IP level socket options are defined differently in Winsock.h than in Ws2tcpip.h. In Winsock.h, the definitions are the following:

/*
 * Options for use with [gs]etsockopt at the IP level.
 */
#define IP_OPTIONS          1           /* set/get IP per-packet options    */
#define IP_MULTICAST_IF     2           /* set/get IP multicast interface   */
#define IP_MULTICAST_TTL    3           /* set/get IP multicast timetolive  */
#define IP_MULTICAST_LOOP   4           /* set/get IP multicast loopback    */
#define IP_ADD_MEMBERSHIP   5           /* add  an IP group membership      */
#define IP_DROP_MEMBERSHIP  6           /* drop an IP group membership      */
#define IP_TTL              7           /* set/get IP Time To Live          */
#define IP_TOS              8           /* set/get IP Type Of Service       */
#define IP_DONTFRAGMENT     9           /* set/get IP Don't Fragment flag   */
#define IP_DEFAULT_MULTICAST_TTL   1    /* normally limit m'casts to 1 hop  */
#define IP_DEFAULT_MULTICAST_LOOP  1    /* normally hear sends if a member  */
#define IP_MAX_MEMBERSHIPS         20   /* per socket; must fit in one mbuf */

IPPROTO_IP level socket options in Ws2tcpip.h

The options at this level are defined in Ws2tcpip.h as:

/*
 * Option to use with [gs]etsockopt at the IPPROTO_IP level.
*/
#define IP_OPTIONS             1     /* set/get IP options */
#define IP_HDRINCL             2     /* header is included with data */
#define IP_TOS                 3     /* IP type of service and preced*/
#define IP_TTL                 4     /* IP time to live */
#define IP_MULTICAST_IF        9     /* set/get IP multicast i/f  */
#define IP_MULTICAST_TTL       10     /* set/get IP multicast ttl */
#define IP_MULTICAST_LOOP      11     /*set/get IP multicast loopback */
#define IP_ADD_MEMBERSHIP      12     /* add an IP group membership */
#define IP_DROP_MEMBERSHIP     13    /* drop an IP group membership */
#define IP_DONTFRAGMENT        14     /* don't fragment IP datagrams */

Setsockopt or getsockopt runtime error

If you don't correctly match the header and library files, setsockopt or getsockopt may fail with runtime error 10042 (WSAENOPROTOOPT) or the option value you set or get may not be as you would have expected.

Case 1: runtime error 10042 (WSAENOPROTOOPT)

Options that fall into this category include:

• IP_ADD_MEMBERSHIP
• IP_DROP_MEMBERSHIP
• IP_TTL
• IP_TOS

Assume that you intend to join a multicast group by running code that's similar to the following:

#include <stdio.h>
#include <stdlib.h>
#include <winsock.h>

int main(int argc, char* argv[])
{
   ...
   if (setsockopt(sock,
                  IPPROTO_IP,
                  IP_ADD_MEMBERSHIP,
                  (char FAR *)&mreq,
                  sizeof (mreq)) == SOCKET_ERROR)
   {
      printf ("setsockopt failed: %d"), WSAGetLastError());
      closesocket (sock);
      return FALSE;
   }
   ...
}

Case 2: Options set or get don't take effect

Options that fall into this category include:

• IP_MULTICAST_IF
• IP_MULTICAST_TTL
• IP_MULTICAST_LOOP
• IP_DONTFRAGMENT

Take IP_MULTICAST_TTL as an example. In Winsock.h, IP_MULTICAST_TTL is defined as 3. In ws2tcpip.h, the constant is defined as 10 and IP_TOS is defined as 3. Try to change the default TTL value:

#include <stdio.h>
#include <stdlib.h>
#include <winsock.h>

int main(int argc, char* argv[])
{
   int ttl = 7 ; // Arbitrary TTL value.
   ...
   source_sin.sin_family = AF_INET;
   source_sin.sin_port = htons(0);
   source_sin.sin_addr.s_addr = htonl (INADDR_ANY);

    if (bind(sock,
                (struct sockaddr FAR *)&source_sin,
                sizeof(source_sin)) == SOCKET_ERROR)
    {
        printf ("bind() failed: %d"), WSAGetLastError());
        closesocket (sock);
        return FALSE;
    }

    if (setsockopt(sock,
                      IPPROTO_IP,
                      IP_MULTICAST_TTL,
                      (char *)&ttl,
                      sizeof(ttl))) == SOCKET_ERROR)
    {
        printf ("setsockopt failed: %d"), WSAGetLastError());
        closesocket (sock);
        return FALSE;
    }
    ...
}

If you link the project with Ws2_32.lib and run the application, setsockopt with IP_MULTICAST_TTL will succeed. However, the multicast TTL setting won't take effect. If you examine the network trace, you see that the TTL value still remains as 1 (the default).