> On Sep 10, 2018, at 1:51 PM, [email protected] wrote:
>
> Hi there,
> I'm trying to send a single IGMP control packet out of an Intel X550 to its
> connected router.
> I've looked at the packet in wireshark and its absolutely fine, the ethernet
> header, the ip header, the ipchecksum offload and the IGMP payload & checksum
> - there's nothing wrong with it.
> It is 46 bytes formatted and the pkt and data lengths of the allocated buffer
> are all set to 46 bytes. Its a 46 byte packet - end of!
> However.... what comes out of the interface is 60 bytes of data - the 46
> bytes I want to send + 14 bytes of zeros.
> The 14 bytes is curiously equivalent to the size of an ethernet header, but I
> just cannot see how it is just being added on to the end of the packet data.
> Has anyone else observed this effect , or indeed know what's causing it ?
Not sure what you are doing, but the smallest packet on ethernet is 60 bytes +
4 bytes CRC for 64 bytes total. Normally anything less then 60 bytes + CRC is
called a runt packet and are discarded. The NIC is padding the data to 60 bytes
then adds the 4 byte CRC.
Hope that helps.
> Many thanks
> Terry.
Regards,
Keith
