how do I know if a user of website is active by IP, cookie and Session ID

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VB

ASP.NET

Hi All,

I had to block the same user multi login to my website. With the following function I am able to check and block if the same user tries to login again by using a public datatable.
Now for dealing with sessions ended without pressing logout button, can we check if a session is active based upon a user's IP address, and session ID which may be stored in a cookie?

 Public dtExistingUsers As DataTable


Protected Function fnMultipleUserCheck(ByVal UserID)
        fnMultipleUserCheck = 0

	If IsNothing(dtExistingUsers) Then
            dtExistingUsers = New DataTable
            dtExistingUsers.Columns.Add("Session_UserName")
            dtExistingUsers.Columns.Add("Session_IP")
            dtExistingUsers.Columns.Add("Session_ID")
        End If

	For Each row As DataRow In dtExistingUsers.Rows
            If row.Item("Session_UserName") = UserID Then
                fnMultipleUserCheck = 1
            End If
        Next

	If fnMultipleUserCheck = 0 Then
	    Dim newrow As DataRow = dtExistingUsers.NewRow
            newrow.Item("Session_UserName") = UserID
            newrow.Item("Session_IP") = System.Web.HttpContext.Current.Request.UserHostAddress
            newrow.Item("Session_ID") = HttpContext.Current.Session.SessionID
            dtExistingUsers.Rows.Add(newrow)
	End If

	 Return fnMultipleUserCheck
    End Function

Thanks