I made some minor changes to my nginx server using a Linux VPS running FreeBSD 10.3 with TLS, ciphers and then file caches. Except for the file caching, I had done these changes before without issue. I went away for the weekend and, when I came back, netstat -i showed Idrop as being 48665. The web sites on this server don't exhibit any problems that I can see.
I reverted all my changes back to their original but I still see the same value for Idrop and it never changes from day to day or throughout the day. All the other values change accordingly.