Thanks a lot for this posting!
It helped me solve a bunch of problems with a customer site (running some exotic switching infrastructure).
Problems we had with "options ip.fastpath.enable on":
- cifs setup (AD join) did not work reliably
- CIFS/SSH/HTTP access from Windows NLB (network load balancing) node did not work reliably
- probably other side effects we did not explicitly notice
All issues were gone by setting it to "off", no restart required.
Thanks again!