Editing Internet security (section)

=== Firewalls ===
{{Main|Firewall (computing)}}

A [[firewall (computing)|computer firewall]] controls access to a single computer. A network firewall controls access to an entire network. A firewall is a security device — computer hardware or software — that filters traffic and blocks outsiders. It generally consists of gateways and filters. Firewalls can also screen network traffic and block traffic deemed unauthorized.

====Web security====
Firewalls restrict incoming and outgoing [[network packet]]s. Only authorized traffic is allowed to pass through it. Firewalls create checkpoints between networks and computers. Firewalls can block traffic based on IP source and TCP port number. They can also serve as the platform for IPsec. Using tunnel mode, firewalls can implement VPNs. Firewalls can also limit network exposure by hiding the internal network from the public Internet.

====Types of firewall====

===== Packet filter =====
A packet filter processes network traffic on a packet-by-packet basis. Its main job is to filter traffic from a remote IP host, so a router is needed to connect the internal network to the Internet. The router is known as a [[screening router]], which screens packets leaving and entering the network.

===== Stateful packet inspection=====
In a [[stateful firewall]] the [[circuit-level gateway]] is a [[proxy server]] that operates at the network level of an [[OSI model|Open Systems Interconnect (OSI) model]] and statically defines what traffic will be allowed. Circuit proxies forward [[network packet]]s (formatted data) containing a given port number, if the [[Port (computer networking)|port]] is permitted by the [[algorithm]]. The main advantage of a proxy server is its ability to provide [[Network Address Translation]] (NAT), which can hide the user's IP address from the Internet, effectively protecting internal information from the outside.

===== Application-level gateway =====
An [[application-level firewall]] is a third-generation firewall where a [[proxy server]] operates at the very top of the OSI model, the [[Internet protocol suite|IP suite]] application level. A network packet is forwarded only if a connection is established using a known protocol. Application-level gateways are notable for analyzing entire messages rather than individual packets.