detection of machines behind PF firewall

[alexander lind]

Hi all

Is there currently any known method for detecting information about a  
machine behind a PF firewall?

Specifically, if I have a machine with two IP addresses, is it  
possible for a remote attacker to detect that these two IP addresses  
are bound on the same machine  (this machine would be behind a PF  
firewall with the scrubbing option). The two IP addresses would be  
known to the attacker.

Thanks
Alec