> MTU=4 does not even make for a proper IPv4 packet, for which > the minimum reasonable MTU would be the IPv4 header size. the minimum size of ipv4 header is 20 bytes, the ethernet protocol use mtu=16byte, so the sentence below is not valid (imho)...i can build a layer2 protocol where the mtu is 4 bytes: IP protocol must be able to work above my layer2 >>sk_buff len: 24 >>!!!fragmented!!! >>frag off: 0 >> >>sk_buff len: 24 >>!!!fragmented!!! >>frag off: 0 > > This might be the reply. no, it is impossibile because i've no response with that line of hping (i send only one packet, zero receive): infact the output is: --- localhost hping statistic --- 1 packets tramitted, 0 packets received, 100% packet loss (0 received --- READ THE WHY BELOW ) > Input only, and empty fragment. You ought to check the packet size the packet size is 40 bytes.... BELOW: but...maybe i've found the "solution"...but i've to test it yet. So: i've a 40 bytes packet, and a MTU of 4 byte. the payload size is 20 byte (because hping use the smaller ipheader: 20bytes). At this point the fragment's number is -inevitably- 20/4 = 5. But, how can i calculate the fragment offset? In this way: the first packet has fragoff = 0, the second packet has fragoff = size of the first fragment / 8 = 0!!! (rounded down), the third packet has fragoff = (size of the first fragment+size of the second fragment) / 8 = 1... That's why i have no packet received, because i can't defragmented a packet with some frags that have the same fragoff! So in this way we have explained: 1. why i haven't receive a response packet 2. why i have the same fragoff it's all ok, now. what do you think Jan? -- Nicola Padovano e-mail: nicola.padovano@xxxxxxxxx web: http://npadovano.altervista.org -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
