Port Address Translation, Proxy Firewall, Proxy Types

Port Address Translation, Proxy Firewall, Proxy Types

Port Address Translation (PAT)

An extension to network address translation (NAT), which translates all addresses to one externally routable IP address, is to use port address translation

Proxy Firewall

A proxy firewall mediates communications between untrusted endpoints (servers/ hosts/clients) and trusted endpoints (servers/hosts/clients). From an internal perspective, a proxy may forward traffic from known, internal client machines to untrusted hosts on the internet, creating the illusion for the untrusted host that the traffic originated from the proxy firewall, (PAT) to translate the source port number for an external service. The port translation keeps track of multiple sessions that are accessing the internet.

thus, hiding the trusted internal client from potential attackers. To the user, it appears that they are communicating directly with the untrusted server. Proxy servers are often placed at internet gateways to hide the internal network behind one IP address and to prevent direct communication between internal and external hosts.

Circuit-Level Proxy

A circuit-level proxy creates a conduit through which a trusted host can communicate with an untrusted one. This type of proxy does not inspect the data field that it forwards, which adds very little overhead to the communication between the user and untrusted server.

The lack of application awareness also allows circuit-level proxies to forward any traffic to any TCP and UDP port. The disadvantage is that the data field will not be analyzed for malicious content.

Application-Level Proxy

An application-level proxy relays the traffic from a trusted endpoint running a specific application to an untrusted endpoint.

The most significant advantage of application- level proxies is that they analyze the data field they forward for various sorts of common attacks such as buffer overflows. Application-level proxies add processing overhead.