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4/8/2010

This code sample finds a route in the table and changes its metric to NewMetric. The metric change must be viable otherwise TCP/IP will not accept it.

Copy Code 
   PMIB_IPFORWARDTABLE pIpForwardTable = NULL;
   ULONG dwSize = 0;
   BOOL bOrder = FALSE;
   DWORD dwStatus = 0;
   DWORD Dest = 0xDDCCBBAA; // this is in host order Ip Address
AA.BB.CC.DD is 0xDDCCBBAA
   DWORD NewMetric = 3;

   // Find out how big our buffer needs to be
   dwStatus = GetIpForwardTable(pIpForwardTable, &dwSize,
bOrder);
   if (dwStatus == ERROR_INSUFFICIENT_BUFFER) {

	// Allocate the memory for the table
	if (!(pIpForwardTable = (PMIB_IPFORWARDTABLE)malloc(dwSize)))
{
		 OutputMessage(TEXT("Malloc failed, Out of Memory!\r\n"));
		 exit(1);
}

	// Now get the table
	dwStatus = GetIpForwardTable(pIpForwardTable, &dwSize,
bOrder);
   }

   if (dwStatus != ERROR_SUCCESS) {
	OutputMessage(TEXT("GetIpForwardTable Failed, ERROR %d\r\n"),
dwStatus);
	if (pIpForwardTable) 
		 free(pIpForwardTable);
	exit(1);
   }
   
   // Search for the row in the table that is wanted.
   for (unsigned long int i=0; i <
pIpForwardTable->dwNumEntries; i++) {
	if (pIpForwardTable->table[i].dwForwardDest == 0x0000389D)
{
		 
		 pIpForwardTable->table[i].dwForwardMetric1 = 3;

		 // Delete the old default gateway entry
		 dwStatus =
SetIpForwardEntry(&(pIpForwardTable->table[i]));

		 if (dwStatus != ERROR_SUCCESS) {
			OutputMessage(TEXT("Could not change route metric\n"));
			exit(1);
		 }
}
   }		 

   if (dwStatus == NO_ERROR)
	OutputMessage(TEXT("Metric changed successfully\n"));
   else if (dwStatus == ERROR_INVALID_PARAMETER)
	OutputMessage(TEXT("Invalid Parameter\n"));
   else 
	DisplayErrorMessage(dwStatus);

   // Free resources
   if (pIpForwardTable) 
	free(pIpForwardTable);

See Also