reverso-test detects interfaces which are physically looped back, such that packets exiting the interface immediately arrive back on that interface.

Run it on an illumos machine with an interface name, e.g.

BRM06240009-switch # ./reverso-test gimlet27
Success: loopback detected
BRM06240009-switch # ./reverso-test gimlet2
Error: No loopback detected

In this system, the gimlet27 cubby has a Reverso board installed, while gimlet2 does not.