Private IP uses as external/public

[mariat]

I have a question, I am using visualroute tool and we have this internal IP address (192.168.1.5) that somebody is using and I just need to know who/what machine.....It suppose to be inside the company, my network configuration is really basic:
line -> router/gateway -> firewall -> switch
we use 192.168.1.x with 255.255.255.0
If I disconnect the firewall from the router/gateway I lost contact with the 192.168.1.5 (it is not answering the pings)
When I do the traceRoute, shows me:
from my machine goes to -> router -> ISP wan IP address -> 192.168.1.5
How does the private IP address can be public?......Thanks for any help

 

[routerman]

Can you use `NBTSTAT -A 192.168.1.5' from a command prompt, should give you the logged on user name?

 

[mojo31]

Or check your DNS/Wins entries against the IP.

 

[mariat]

I did "nbtstat -A 192.168.1.5" and "nbtstat -a cobra" and I am getting the same answer:
"Host not found"
Also I checked the DNS entries and yes I have an entry for this IP, this was a valid IP address used before by an user and notice the problem when the user has the computer off and I was getting answers to the ping, so I change the IP address of the user for something else and start tracing the 192.168.1.5......We use static IP.
We use NAT on the firewall, so I do not understand why the firewall goes outside to the router and to the WAN IP, at least the firewall or router should know this is a private address not public.

Thanks for any light