I have inherited a network that has a proxy appliance. One side of the proxy appliance is plugged into the LAN and the other into the Firewall. Some of the client machines on the network are configured with proxy details in their browser and everything works as normal.
Some of the users do not have proxy details but they can still get out on the web. They are using a default gateway of the router that is attached to the proxy appliance. Regardless of what way the proxy appliance is setup I am confused as to how the users can even find the firewall! even if the proxy appliance is incorrectly configured and wide open I would have thought no one should be able to contact the firewall as it is not directly plugged into the LAN.
Any ideas how I can see how this is occuring. I have checked arp tables wireshark etc.