On Wed, Nov 28, 2018 at 7:53 PM Cong Wang <xiyou.wangc...@gmail.com> wrote: > > On Wed, Nov 28, 2018 at 7:50 PM Eric Dumazet <eduma...@google.com> wrote: > > > > On Wed, Nov 28, 2018 at 7:40 PM Cong Wang <xiyou.wangc...@gmail.com> wrote: > > > > > > On Wed, Nov 28, 2018 at 4:07 PM Eric Dumazet <eduma...@google.com> wrote: > > > > > > > > A NIC is supposed to deliver frames, even the ones that 'seem' bad. > > > > > > A quick test shows this is not the case for mlx5. > > > > > > With the trafgen script you gave to me, with tot_len==40, the dest host > > > could receive all the packets. Changing tot_len to 80, tcpdump could no > > > longer see any packet. (Both sender and receiver are mlx5.) > > > > > > So, packets with tot_len > skb->len are clearly dropped before tcpdump > > > could see it, that is likely by mlx5 hardware. > > > > Or a router, or a switch. > > > > Are your two hosts connected back to back ? > > Both should be plugged into a same switch. I fail to see why a > switch could parse IP header as the packet is nothing of interest, > like a IGMP snooping.
Well, _something_ is dropping the frames. It can be mlx5, or something else. Does ethtool -S show any increasing counter ?
