code for dropping packets at a particular port using VB

Question

this code is supposed to be used in VB. port number and IP address is available. how to prevent packets from entering is to be known. Its similar to the work a FireWall does.

Answer 1

Ur own Personal FIREwall!!

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Here is some sample VB6 code to get You started.

It makes use of the winsock control to open and connect to a port itself.

Thereby it automatically denying access to port by other process.

Public Type MIB_TCPROW
dwState As Long
dwLocalAddr As Long
dwLocalPort As Long
dwRemoteAddr As Long
dwRemotePort As Long
End Type

Public Type MIB_TCPTABLE
dwNumEntries As Long
table(100) As MIB_TCPROW
End Type

Public MIB_TCPTABLE As MIB_TCPTABLE

Public Declare Function GetTcpTable Lib "iphlpapi.dll" (ByRef pTcpTable As
MIB_TCPTABLE, ByRef pdwSize As Long, ByVal bOrder As Long) As Long
Public Declare Function SetTcpEntry Lib "IPhlpAPI" (pTcpRow As MIB_TCPROW)
As Long
Public Declare Function ntohs Lib "WSOCK32.DLL" (ByVal netshort As Long) As
Long


Public Sub BlockPort


Dim LTmp As Long
Dim x As Integer, i As Integer, n As Integer
Dim RemP As String
Dim tcpt As MIB_TCPTABLE

LTmp = Len(MIB_TCPTABLE)
GetTcpTable tcpt, LTmp, 0
x = tcpt.dwNumEntries

For i = 0 To tcpt.dwNumEntries - 1

RemP = ntohs(tcpt.table(i).dwRemotePort)

If RemP = "8080" And tcpt.table(i).dwState <> 2 Then
tcpt.table(i).dwState = 12
SetTcpEntry tcpt.table(i)
End If

Next i

End Sub

If you are looking an easier way to block a single port then :

• Use a Winsock Control in your VB form.

• Set its localport property to the port number you want to block

Complete reference of Winsock for VB6 here

...and Thats IT!! Your own personal firewall is up!!

GoodLUCK!!
- CVS