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Using Vista and Windows 7 Firewall from Visual C++

September 09, 2009

In Vista the Firewall API changed a lot in comparison to the previous versions.

You can drive the Windows Firewall using a COM API, a layer over the Windows Filtering Platform. If you are thinking to develop directly the WFP, it's better to change your idea. WFP is a low level API to build Firewalls and not to be managed directly from traditional applications.

On the other side it's a long time that Visual C++ ship with the powerful #import directive that can save you a lot of time in COM client applications.

The starting point to use the firewall API in a Visual C++ project is the following statements in the stdafx.h:

#import "netfw.tlb" rename_namespace("fw")
#include <Netfw.h>

The import statement trigger the creation of two files:

  • netfw.tlh contains things like strong typed smartpointers for the types in the type library (_COM_SMARTPTR_TYPEDEF), enums and interface declarations
  • netfw.tli contains methods that wraps calls and throws exceptions in place of HRESULTs.

The rename_namespace directive is the way you can choose the C++ namespace name for all the code created in those two files, in our case "fw".

Using the COM API is now very simple. Let's see how to list the firewall rules:

typedef BOOL (*RuleCallback)(fw::INetFwRulePtr& Rule);

void ListRules(RuleCallback Callback)
  // Connect to the firewall
  fw::INetFwPolicy2Ptr Pol2;
  hr = Pol2.CreateInstance(__uuidof(fw::NetFwPolicy2));
  if(Pol2 == NULL)

  // Retrieve collection rules
  fw::INetFwRulesPtr Rules = Pol2->Rules;
  if(Rules == NULL)

  // enumerate the collection and call a callback function
  ULONG num;
  VARIANT obj;
  IEnumVARIANTPtr enumerator = Rules->Get_NewEnum();
  while(enumerator->Next(1, &obj, &num) == S_OK)
      fw::INetFwRulePtr Rule = obj;

Adding, deleting, and working on service rules, is again very simple. The attached file contains a working Visual C++ 2008 sample with all those functions.

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