Understanding GTP Message-Length Filtering
You can configure the device to drop packets that do not meet your specified minimum or maximum message lengths. In the GPRS tunneling protocol (GTP) header, the message length field indicates the length, in octets, of the GTP payload. It does not include the length of the GTP header itself, the UDP header, or the IP header. The default minimum and maximum GTP message lengths are 0 and 65,535 bytes, respectively.