What is Firewall
A Firewall is a device or software package that provides a secure gateway
between two networks. Some network devices such as routers have firewalls built
in. There are also 'personal firewalls' that do the same job but only protect
one system (such as a laptop or PC).
Firewalls ensure that certain network traffic (e.g. from certain
applications) is allowed to pass from one network to another according to a set
security policy. Firewalls can prevent network-based attacks that are often
targeted against systems.
Firewalls can log connection attempts and traffic and authenticate users
trying to make network connections. They can inspect network packets, e-mail
viruses and web pages, and track the state of connections to ensure they are
behaving as expected. Firewalls also protect internal networks by performing
Network Address Translation (NAT). Firewalls fall into three main types:
Stateful Inspection, Application Proxy or Packet Filtering.
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