I'm trying to practice penetration testing on my home network. The target system is my desktop computer, which is connected to the network via ethernet cable. The attack system is my laptop, which is connected via Wi-Fi. My laptop is running Ubuntu Linux 12.10.
I'm simulating an attack by someone who has gained access to the wireless network, but is interested in data that resides on a particular computer which happens to be on the wired portion of the network - my desktop. In this scenario (foregoing any further knowledge I have about my network or the target system) I'm having a hard time finding the IP address of my desktop.
Tools such as ipscan or nmap only appear to find devices on the wireless side of the network. I know I could go to the router, and pull up the list of connected devices, but that would require foreknowledge (or cracking) of the router's password - something I'm pretending to not have at this point.
In this scenario, how can I use my laptop to find my desktop on the network and establish a connection? Again, I'm simulating the role of an outside attacker who's just gotten access to the Wi-Fi - all I know is the Wi-Fi SSID, Wi-Fi PSK, Wi-Fi AP's MAC address, and the network's gateway address.