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Network fundamentals

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.
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Sid_F
Asked:
Sid_F
3 Solutions
 
pony10usCommented:
If the firewall is physically isolated (only connection is to the proxy appliance) then it is not possible to bypass the proxy.  Even though the information is not supplied in the browser settings.

If you have the proxy blocking/filtering a specific website then try to get to that site both with the proxy settings in place and not. You should be blocked both ways.
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SurranoSystem EngineerCommented:
sounds like the proxy acts as an ordinary gateway between LAN and the firewall. Try to traceroute (*nix) or tracert (windows) the firewall's IP and check the routing tables as well on a machine that "bypasses" the proxy and see how it is routed.
If it is routed through the proxy then the proxy acts as a gateway (it shouldn't).
If it is routed through different nodes then you'll see where to look for the gateway.
If the gateway is accessed directly (i.e. listed as first and only hop in traceroute) then it is on the same LAN as the clients and whatever switches/routers are in place should segregate them.
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amatson78Sr. Security EngineerCommented:
I would recommend running Packet Captures on the firewall and proxy appliance to see if and how traffic is flowing through the proxy. What type of proxy appliance is this? Are there any other cable terminations from the firewall to the LAN? The proxy may just be routing traffic, what is the route table of the proxy?

Cheers,
Alan
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Sid_FAuthor Commented:
Thanks
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