VB:将IP转换成IP段

怎么将IP转换成IP段，
当Text1内的IP显示为：202.188.55.55
则Text2内显示为：202.188.55.1-202.188.55.255
当Text1内的IP改变为：60.47.66.66
则Text2内追加显示为：202.188.55.1-202.188.55.255
  60.47.66.1-60.47.66.255

VB code

Private Sub Command1_Click()
Dim s As String, s1 As String
s1 = Text1.Text
s = Right(s1, 3)
If Len(s) = Len(Replace(s, ".", "")) Then
    Text2.Text = Left(s1, Len(s1) - 3) & "1-" & Left(s1, Len(s1) - 3) & "255"
Else
    s = Left(s, InStr(s, "."))
    Text2.Text = Left(s1, Len(s1) - 3) & s & "1-" & Left(s1, Len(s1) - 3) & s & "255"
End If
End Sub