squid proxy firewall
folks, is the Squid a proxy firewall (or application layer firewall)??
Third generation - application layer
... application layer firewall, also known as a proxy-based firewall...
The key benefit of application layer filtering is that it can "understand" certain applications and protocols (such as File Transfer Protocol, DNS, or web browsing), and it can detect whether an unwanted protocol is being sneaked through on a non-standard port or whether a protocol is being abused in a known harmful way...