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Proxy and Tunneling

Posted on 2014-04-01
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Last Modified: 2014-04-01
I assume the following is true:

I would be ill advised to tunnel (as in SSL) at the application level, but proxy in the DMZ

... because if you tunnel at the app level, as the packets leave the app to the DMZ where the proxy is, the proxy can not truly collect the packets into a message, and based upon the content of that message make decisions, like blocking IP's  from going to certain destinations, or in the case of incoming messages, blocking IP's from coming in.

Therefore you either want to proxy and tunnel at the DMZ level, or proxy and tunnel at the app level, but not proxy at the DMZ, and tunnel at the app level

Is this correct?
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Question by:Anthony Lucia
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Expert Comment

by:Rich Rumble
ID: 39970034
You seem to be very interested in proxies and DMZ's... I think your definition of DMZ may be incorrect however. The DMZ is an isolated Network, not a layer in the TCP/IP or OSI stacks, like Application, Link, and Transport etc...
Let's put it this way, a http proxy that scans the traffic for malicious content cannot scan httpS connections, UNLESS the proxy injects it's own SSL certificate between the Client and itself. Effectively the proxy is translating between the two, the end website and the client.
SSL traffic operates at two different layers of the two standard stacks
The SSL/TLS library operates above the transport layer (uses TCP) but below application protocols. In the OSI model it's at layer 6 (presentation).
In both however you can fully view/read the IP information so decisions can still be based on DNS or IP addresses, but not the content unless that content is intercepted and then passed on.
-rich
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Author Comment

by:Anthony Lucia
ID: 39970109
OK, a proxy cant filter out content unless it scans the data.

So why would a proxy NOT scan the data.  IF it doesn't scan the data, wouldn't you simply replace it with port forwarding ?
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Rich Rumble earned 500 total points
ID: 39970152
If the content is encrypted, it looks like jibberish. So to get a http proxy to scan httpS secured traffic, the PC has to trust the SSL cert the Proxy uses, and that way the data between the host and the proxy is encrypted, and the proxy can decrypt that traffic, then the proxy makes a connection to where the PC wanted to go, and now the proxy and Gmail (for example) can talk in a way that the proxy can inspect. Think of the proxy as a man in the middle.
The proxy can see IP data not matter what, even if it's not reading the content, the IP is not encrypted otherwise it would not get where it's going. You can make decisions based on IP data, and or DNS data, but unless you can decrypt and look at the contents, you can't really make decisions on content.
An AV-Proxy is like the TSA or Airport screener, using an x-ray machine to look at the contents of your luggage. based on what is seen, actions can be taken. In the case of SSL, it's like putting a lead safe on the belt, if you don't open it for the screener, they will never know what's in it. Trusting the cert from a proxy is like giving the screener a skeleton key that will open any safe that is put on the belt.
-rich
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