What is a Perimeter Firewall?

Over 30 years ago, the concept of a firewall entered the IT security conversation. Today, technology still plays a vital role in enterprise security, facilitating secure connectivity between different networks. As a mechanism of filtering out malicious traffic before it crosses from a public network into a private network, a perimeter firewall has ascertained its merit over the decades. As with any persistent technology, it has obviously spawned many iterations. In this post, discover how a perimeter firewall prevents network intrusions.

What is a Perimeter Firewall?

A perimeter firewall is a network security device that acts as the primary defense mechanism protecting an organization’s internal network from unauthorized external access. It is strategically placed at the network’s edge, where it connects to external networks, including the Internet, other corporate branches, or partner networks. Its primary function is to filter incoming and outgoing traffic based on a set of stringent security rules and policies determined by network administrators.

Perimeter firewalls operate by inspecting data packets that attempt to enter or leave the network. These inspections are based on predefined criteria such as source and destination IP addresses, port numbers, and the type of protocol used (TCP, UDP, ICMP, etc.). The firewall then decides whether to allow or block these packets based on its rule set, which is designed to minimize the risk of cyberattacks such as hacking, malware infections, and denial-of-service attacks.

Modern perimeter firewalls are more advanced and incorporate features like stateful inspection, which tracks the state of active connections and makes decisions based on the context of traffic and packets rather than just inspecting packet headers. Some may also include integrated intrusion prevention systems (IPS), which actively detect and prevent attacks by analyzing traffic for known threat patterns.

Perimeter firewalls can be hardware-based, which often provides higher performance and additional features like VPN support and dedicated security processing units, or software-based, which offers more flexibility and easier integration with cloud services. They are a critical component of any organization’s security architecture, providing a crucial checkpoint for traffic and acting as a deterrent against external threats.

How does it work?

A perimeter firewall works as a filter between a company’s internal network and external, untrusted networks like the Internet. It scrutinizes all inbound and outbound network packets and allows or blocks them based on pre-established security rules. The perimeter firewall typically makes this decision by examining packet headers, which include source and destination IP addresses, port numbers, and protocol types.

In an enterprise setting, a perimeter firewall often uses complex algorithms to analyze the state of active connections. It uses stateful inspection to track the state of network connections—such as whether they are new, established, or related to existing connections—and makes access decisions accordingly. This method ensures incoming packets are part of an ongoing conversation, rather than unsolicited attempts to access the network.

Modern perimeter firewalls can also perform deeper inspections, including examining the payload of packets for known threats or anomalies. Deep packet inspection (DPI) is crucial for identifying and mitigating sophisticated cyber threats that may otherwise bypass basic security checks.

Benefits of a Perimeter Firewall

A perimeter firewall defines and enforces the boundary between a public and private network. Perimeter firewalls have both their benefits and their limitations to an organization’s overall security posture.

Some of the benefits:

• Network Traffic Visibility: It has visibility into all traffic entering and leaving the private network. This not only enables corporate security but also provides valuable information about the use of internal and external services.
• Malicious Content Filtering: An NGFW (Next-generation Firewall) deployed as a perimeter firewall can identify and block malware and other attacks from entering an organization’s network.
• Improved User Privacy: Perimeter firewalls can enhance user privacy by acting as a proxy between internal users and external servers.
• Data Loss Prevention: Perimeter firewalls can help to prevent the loss of sensitive and valuable data by identifying and blocking traffic that does not comply with company policy.

Perimeter firewall risks

A perimeter firewall can possibly be infiltrated by unknown devices that connect from outside the network, including the laptops and mobile devices of users and employees. Also, as businesses migrate their operations to the cloud, they have to make sure they adapt their defense to protect their infrastructure against attackers who target cloud architectures found in data centers, Software-as-a-Service (SaaS) providers, and other cloud computing systems.

In addition, when a company opens up its network to interface with another through the internet, it can also possibly allow malicious code or an unauthorized individual into its network. Also, insider attacks may not be detected by a perimeter firewall because the malicious data originates from behind the firewall. Therefore, a firewall should be just one component of a larger network security plan.

What is the difference between Perimeter Firewalls and Data Center Firewalls?​

Data Center Firewall is a stateful, multitenant, network layer, 5-tuple (protocol, source, and destination port numbers, source and destination IP addresses) Software Defined Networking (SDN) firewall. The Data Center Firewall safeguards traffic flows east-west and north-south across the network layer of virtual networks and regular VLAN networks.

Data center firewalls are designed to protect virtual computers, as opposed to network perimeter firewalls. They are also intended for the agility that data centers require, allowing managers to reallocate virtual resources as they see appropriate without violating firewall restrictions.

Conclusion

A perimeter firewall is a network security device positioned at the boundary between an organization’s internal and external networks that primarily monitors and controls incoming and outgoing network traffic based on predetermined security rules. Perimeter firewalls work by inspecting packets, filtering them based on predefined rules, performing SPI on them, controlling their access, logging and reporting the analysis results, and performing other built-in security measures. Using perimeter firewalls lets organizations control access, protect against external threats, segment networks, enhance privacy and confidentiality, comply with regulations, log and monitor incidents, and implement flexible security policies.