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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. <br />
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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! &nbsp;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.<br />
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Any ideas how I can see how this is occuring. I have checked arp tables wireshark etc.
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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.

Network fundamentals

Hardware-based firewalls provide more sophisticated protection for inbound and outbound traffic than the simple Windows software firewall or the basic NAT firewalls found in routers. These devices implement techniques such as stateful packet inspection, deep packet inspection, and content filtering; and may include built-in antivirus and anti-malware protection.

Hardware Firewalls

The Windows operating systems have distinct methodologies for designing and implementing networks, and have specific systems to accomplish various networking processes, such as Exchange for email, Sharepoint for shared files and programs, and IIS for delivery of web pages. Microsoft also produces server technologies for networked database use, security and virtualization.

Windows Networking

Networking is the process of connecting computing devices, peripherals and terminals together through a system that uses wiring, cabling or radio waves that enable their users to communicate, share information and interact over distances. Often associated are issues regarding operating systems, hardware and equipment, cloud and virtual networking, protocols, architecture, storage and management.