Dim Rws As Long, Rng As Range, c As Range

    Rws = Cells(Rows.Count, "A").End(xlUp).Row

    Set Rng = Range(Cells(1, 1), Cells(Rws, 1))

    For Each c In Rng.Cells
        If c = "," Then c.Offset(0, 7) = "=IF(RC[-7]="","",CONCATENATE(""network "",""IpAnd(A1,B1)"",255-RC[-5],""."",255-RC[-4],""."",255-RC[-3],""."",255-RC[-2]))"
    Next c
When you have the correct formula in a cell, use your macro recorder, click on the cell then hit F2 to edit it. Then hit enter, this is what your formula will be in VBA.