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Perimeter firewall

(also network firewall)

Perimeter firewall definition

A perimeter firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. It forms a barrier around the network perimeter, protecting it from unauthorized access. Unlike internal firewalls, perimeter firewalls are positioned at the edge of an enterprise network, scrutinizing all the traffic that enters or exits.

See also: network security protocols, VPN firewall, firewall, network intrusion protection system

Perimeter firewall examples

  • Enterprise protection: Perimeter firewalls are used by businesses to protect their internal networks from threats originating outside their network. They may also implement application control, intrusion prevention, and VPN support.
  • Service providers: Internet service providers (ISPs) use perimeter firewalls to provide their clients a base level of security and safeguard their own infrastructure.

Advantages and disadvantages of perimeter firewalls


  • Network-wide protection: Perimeter firewalls provide a first line of defense against external threats, protecting the entire network.
  • Traffic control: They allow an organization to control which types of traffic are allowed in and out of the network based on policy rules.


  • Limited internal control: While excellent at blocking external threats, they do not control or protect against threats within the network.
  • False sense of security: They may give an impression of total security, leading to neglect of other crucial security measures.

Using perimeter firewalls

  • Perimeter firewalls should be part of a layered security approach, including internal firewalls, antivirus software, and intrusion detection systems.
  • To provide effective security, regular maintenance and rule updates are essential for perimeter firewalls.