How to fix split text in texbox vb.net ?

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VB

VS2012

Hi all i try to past IP in 1 textbox and when i press OK he mus split in 4 pices like that
123.123.123.123 and split in textbox1,2,3,4 like [123] [123] [123] [123] all is ok but if i put more numbers 123.123.123.123.123.123.123 i get errors can you hel me please ?

Dim str As String = TextBox1.Text
Dim splitStr As String() = str.Split(".")
TextBox1.Text = splitStr(0).ToString()
TextBox2.Text = splitStr(1).ToString()
TextBox3.Text = splitStr(2).ToString()
TextBox4.Text = splitStr(3).ToString()