This field must be validated by a receiving host and if not valid, the datagram will be discarded and no error message will be sent to the sending host. RFC 1121 states that the datagram must be silently discarded if an invalid value is discovered. So, crafting a datagram with an invalid IP version would serve no purpose other than to test if the receiving host complies with the RFC. | Network Traffic Analysis Using tcpdump Examination of Datagram Fields II Judy Novak Johns Hopkins University Applied Physics Laboratory jhnovak@ 1 All material Copyright Novak 2000 2001. All rights reserved. 1 IP Header Fields 2 This page intentionally left blank. 2 IP Header 0 15 16 31 4-bit version 4-bit IP header length 8-bit TOS 16-bit total length in bytes 16-bit IP identification number 3-bit flags 13-bit fragment offset 8-bit time to live TTL 8-bit protocol 16-bit header checksum 32-bit source IP address 32-bit destination IP address options if any 20 byt ïs data 3 This page intentionally left blank.
