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Creating a FireWall Program

Original post by mjwsoft at

The Question :

Is it possible to program an AV or Firewall in VB Express 2005?

The Accepted answer by Martin Xie - MSFT

Hi mjwsoft,

I agree with spotty. C++ may be more suitable for programming Firewall.

If you wish to do it in VB.NET, you need to P/Invoke Packet Filtering API.

The Firewall service usually is based on packet filtering technology.

Here are some references.

1. Simple Packet - Filter Firewall

Working of firewall is based on the following steps:

  • Extract the packet header
  • Check the protocol associated
  • Compare with the rules
  • Check the source and destination add. If protocol is same
  • Check out the port if protocol is TCP
  • Drop or pass the packet

2. Packet Filtering API on MSDN

Packet Filtering API allow us to associate filters to IP adapter interfaces. We can implement a functionality similar that included in TCP/IP filter options in TCP/IP properties of a network adapter.

3. Packet Filtering in .NET

Class library to implement packet filtering funcionality in your .NET applications

4. In addition, here is a Firewall SDK which helps deveopers create and manage a firewall control easily.

The Gtfctrl.dll wraps all the firewall operations in one "Firewall Panel", it can be used in VB.Net , C#.Net.

5. You also can find some ideas in this thread.

How to build a firewall like AVG Firewall in c#

6. The basics of a firewall

Best regards,



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