Screened Host Architecture

This architecture consists of two host machines: a Screening Router and a Screening Host. Screening Router is placed between a local network and the Internet. Its purpose is to block all direct communication between two networks. Only traffic that is allowed to pass through is that coming from the host machine and destined for the Internet or coming from the Internet and destined for the host machine.

Screened Host is the only machine that can be accessed from the Internet and usually runs proxy applications for allowed services. Other hosts on the intranet must connect to proxy service on the host machine in order to use the Internet.This architecture is more flexible than Dual Homed Host architecture. In this setup if a proxy application does not exist for some secure service it can be allowed to pass through the screening router directly to the client on the local network .

 Advantages

•Provides better security and filtering rules are simple
•Provides transparent outbound access and restricted inbound access

 Disadvantages

•If proxy application does not exist for some service logins have to be provided to the local users to use that service or to abandon that service completely
•If both host machines are not configured properly to work together it may leave holes in the firewall that can be exploited by the attacker