In computer networking, an application layer firewall is a firewall operating at the application layer of a protocol stack.[1] Generally it is a host using various forms of proxy servers to proxy traffic instead of routing it. As it works on the application layer, it may inspect the contents of the traffic, blocking what the firewall administrator views as inappropriate content, such as certain websites, viruses, attempts to exploit known logical flaws in client software, and so forth.
An application layer firewall does not route traffic on the network layer. All traffic stops at the firewall which may initiate its own connections if the traffic satisfies the rules.
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