title: What's the practical limit for the data length of UDP packet?
body: <p>This is wikipedia's explanation of the length field of the UDP header:</p>
  
  <blockquote>
    <p>Length<br>
    A field that specifies the length in bytes of the UDP header
    and UDP data. The minimum length is 8 bytes because that is the length
    of the header. The field size sets a theoretical limit of 65,535 bytes
    (8 byte header + 65,527 bytes of data) for a UDP datagram. The
    practical limit for the data length which is imposed by the underlying
    IPv4 protocol is 65,507 bytes (65,535 − 8 byte UDP header − 20 byte IP
    header).</p>
  </blockquote>
  
  <p>The practical limit for the data length should minus 20 byte IP header, why is that?</p>