First of all, lets get the basic information sorted out. Just in case I have it mixed up.

There is an external Firewall - Router (or some such device), and there is an internal Firewall (an application).

Internal firewall also already exists on Windows, but (in Windows 7) it only blocks incoming TCP connections/packets, and not outgoing ones, so I assume an additional software firewall is recommended.

Now, we know of of two basic Firewall filtering techniques:

1.) Network Layer

2.) Application Layer

These techniques have different subcategories:

1.) Network Layer

  1. Stateful
  2. Stateless

2.) Application Layer

  1. Network Based
  2. Host Based

My question is, which filtering technique is used on the external firewall (ie. router) and which type is used on the device (ie. computer).


Edit: Are stateless firewalls still in use?

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    It's impossible to answer, or there will be an answer by firewall provider and by user choice. A boundary firewall can work at application layer (7) when it's a transparent proxy for example. Voting to close as unclear as there's not enough specification to answer right now, it require too much assumption. – Tensibai Feb 10 '17 at 14:48
  • just to clarify, are you saying that any of the above firewall type can be used as the internal or external firewall? – DrDoom Feb 10 '17 at 14:53
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    Yes, that's the point, here we have Layer 7 statefull firewalls at core of the network and on boundaries. Some flows are stateless layer 3, because we're just sending UDP information to a trusted metric system, we don't need to inspect the content of the flow nor to await a feedback from it (for example). – Tensibai Feb 10 '17 at 15:06
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    A level 7 firewall can still do basic tasks as filtering on IP, which is a layer 3 firewall. You should have a look to the OSI model en.wikipedia.org/wiki/OSI_model for an overview, a firewall working at level 7 have to handle level 3 anyway. – Tensibai Feb 10 '17 at 15:18
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    Thanks. I did check the OSI model. I was actually studying this a few years back, but I forgot most of the stuff =) Thanks for the clarifications, and after I wrap my head around all this, I might post another question with more specifics. – DrDoom Feb 10 '17 at 15:35

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