Organization-level rules governing acceptable use of computing resources, security practices, and operational procedures. A proxy is an application running on a gateway that relays packets between a trusted client and an untrusted host. The request appears to originate from the gateway running the proxy, rather than from the client. Thus, the firewall's IP address functions as a proxy address. Not everyone in the industry agrees that a packet-filtering router alone is a firewall.
Many people insist that only a system that includes a dual-homed gateway is a firewall.
The degree to which a screened host may be accessed depends on the screening rules in the router. Also referred to as the demilitarized zone, a screened subnet is a collection of computers that are shielded from both the trusted network and the untrusted network by packet-filtering routers and by gateways. Social engineering attacks are typically carried out by telephoning users or operators and pretending to be an authorized user, to attempt to gain illicit access to systems. To perform this task, this firewall relies on packet-filtering algorithms to examine and compare each packet against known bit patterns of authorized packets. A router or system capable of routing traffic by encrypting it and encapsulating it for transmission across an untrusted network, for eventual de-encapsulation and decryption.