This document discusses corporate firewalls, including what they are, common types, popular products, and limitations. A firewall is a system used to prevent unauthorized access to a private network from the internet. There are several types, including packet filters, application gateways, and circuit-level gateways. Popular hardware firewall products include Cisco PIX and ASA, while software options include Trustix Enterprise Firewall and WinGate NAT Firewall. However, firewalls cannot detect all threats and additional security tools like intrusion prevention systems may be needed to fully screen network traffic contents.

1. How Corporate Firewalls Work
What is a Firewall ?
Types of Firewall
Main fire wall product
Impossible things of Firewall

2. What is a Firewall ?
The system to prevent invading a computer network in the
organization from outside. The computer in which such
system was included. The cracking act which tries to invade
the inner computer network from outside was compared to a
fire. An expression as a “firewall” is being employed as the
one which stops that.

3. Types of Firewall
There are several types of firewall techniques:
Packet filter: Looks at each packet entering or leaving the
network and accepts or rejects it based on user-defined rules.
Application gateway: Applies security mechanisms to specific
applications, such as FTP and Telnet servers.
Circuit-level gateway: Applies security mechanisms when a
TCP or UDP connection is established.
Proxy server: Intercepts all messages
entering and leaving the network.

4. Main fire wall product
The software type
● Trustix Enterprise Firewall
● USP Secure Entry Serveer
● Visionys AirLock
● WinGate NAT Firewall
● Symatec Client Security
The hardware type
● Blue Reef Sonar
● Celestix MSA SeriesCelestix Inc
● Cisco PIX and Cisco ASA
● Clavister
● Symantec Gateway Security

5. Impossible things of Firewall
Even if an attack packet passed by in communication
of the HTTP when HTTP becomes the access
permission, I take it as normal communication by the
firewall. As well as a packet unit, it is necessary to
scan contents of the communication more to defend it.
For a thing carrying this out,
there is a product such as IPS
which is contents filter and
an application firewall,
composition with IDS.

6. Reference
Wikipedia
http://en.wikipedia.org/wiki/
ITmedia
http://www.itmedia.co.jp/enterprise/articles/0411/26/n
ews047_3.html