[dpdk-users] Too much data being sent with small packet and IXGBE

Wiles, Keith keith.wiles at intel.com
Mon Sep 10 22:39:16 CEST 2018

> On Sep 10, 2018, at 1:51 PM, terry.montague.1980 at btinternet.com 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.


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