What NIC card do you have in your system(s) (use sysconfig -ac to get the model number and the card chipset)?
What version of Ontap are you running?
You should check the card slot the NIC is in to make sure you are getting maximum out of the PCIe slot. Some controllers have PCIe x2 and x4 slots for example.
Are you running Jumbo frames from end to end?
The chipset is very important, I believe NetApp only shows drop packets for Chelsio, nothing for Intel or QLogic. Which NIC card you have is very important.
We experienced drop packets recently, it took a while to get the information, we have over 100 7mode controllers (NFS only) most had a fair amount had drop packets. Keep in mind dropping packets on Ethernet connections is common, the amount compared to total packets, if you are you dropping 1 out of 50 million packets, most people consider that reasonable.
If you do a packet capture on the client side (limit the amount of data), use WireShark, go into expert mode, click on Analyze then exprtinfo.
If a NFS client is sending or receiving a fair amount of data and a packet is dropped it can cause the filer to retransmit all of the packets if you set net.ip4.tcp_sack=1 (selective acknowledgement) on the NFS client, then only the dropped packet will be retransmitted. This made a big differences for us on Oracle logwr messages.
I would also look at the NFS mount options for the client machine, you cut down the number of setattr and getattr.
I plan to write up how we gathered our information on dropped packets and the differences in the 10G NIC cards, once I do I will post on this community web page.