my $re = qr{
# match this
( # save to  $1
  \b
  (?&byte)
  (
    \.
    (?&byte)
  ){3}
  \b
)
(?(DEFINE)
  (?<byte>
    2[0-4]\d
    | 25[0-5]
    | 1\d\d
    | [1-9]?\d
  )
)
}x;