My
tutorial is still valid for Mountain Lion.
From looking at some of these configs, it looks like most are omitting the virtual TAP network interface implementation. The TAP interface is required for the hypervisor (Dynamips) <-> Mac host bind. You can't use the physical network interfaces on your Mac (enX) for the bind. Hypervisor-initiated network traffic has to pass thru the TAP interface first before it will get to your Mac host (and the rest of the physical world). Hopefully the following screenshots make this more clear.

