MastaP

lastrev rs b = snd $ maximum [(lst r r, r) | r <- rs, take (length b) r == b] where
    lst [] rest = read rest :: Int
    lst (x:xs) rest = if x /= '.' then lst xs rest else lst xs xs

--*Main> lastrev ["1.3.2.1", "1.3.2.4", "1.3.4.1", "1.3.2.1.2.4", "1.3.2.1.2.30"] "1.3.2.1"
--"1.3.2.1.2.30"